GROWING VEGETABLES IN THE GREENHOUSE - Greenhouse Vegetable Gardening (2015)

Greenhouse Vegetable Gardening (2015)


Vegetables are not only delicious and healthy for you; it’s also great fun to pick a sun-ripened tomato bursting with flavor or a sweet, juicy cucumber right off the vine. While you can grow them outside, the greenhouse environment is a better bet because the harvest will be earlier and more bountiful.

You can follow all the rules to the letter when planting and growing vegetables, or you can make things a bit easier—but then your harvest might not be quite as abundant. There are many ways to go about growing vegetables, ranging from starting the plants from seed to buying mature plants in the garden center. If you’d like to start your plants from seed, check out chapter 4, page 29. Regardless of what growing method you pick, keep in mind that plants have basic requirements and will have to be grown in the greenhouse as they would be grown outside. The procedure described here is gleaned from professional growers’ tips and tricks, which in turn have been adapted to ensure a comfortable atmosphere, all without having to resort to using harmful chemicals.

Grow vertically

Most plants raised in a greenhouse are trained to grow vertically in order to maximize the use of all available space. Tomato, cucumber, melon and bell peppers can be trained with a long strand of twine that reaches all the way up to the ceiling. If you cultivate your crops vertically, the greenhouse becomes like a green arbor and all the plants will benefit from a good supply of light. You’ll have a green jungle to sit and take delight in, as a tomato or cucumber plant can reach a height of more than 4 to 5 meters (13’ to 16’) during a single summer season. Bell peppers and eggplants don’t grow quite as tall and lanky, so they can also be grown as bushes.

The plants can either be grown directly in the ground in the greenhouse, or can be potted in very large containers. While you can use a 10-liter (2.65 gallons) bucket, it’s preferable to use larger pots—the soil tends to dry out more quickly in small pots and containers than in larger sizes. If the plant is potted, place a low growing plant in front of it to prevent the sun from shining directly onto the pot. Attach a nonslip loop of plastic string or twine to the base of the plant stem, being careful to not allow the loop to tighten around the plant and strangle it. Wind the twine around the stem of the plant upwards and towards its top. Move the twine past the plant top and fasten the straight twine tightly around a hook secured to the greenhouse structure. Use removable hooks that can be moved around without a problem—but they need to be the right type for greenhouse cultivation. The wrong kind of hook could become detached from the greenhouse, and make the whole plant collapse when weighed down by its fruit.

You can use common eyebolts for attaching the twine to the greenhouse if the structure is made of wood. Space the eyebolts out evenly—you’ll need one for each plant. Instead of cutting off the twine once it reaches the greenhouse ceiling, leave a length of about 5 m (16’) and loop it in a bundle and tie it together, or tie it securely around a support. Twice a week you’ll add another loop of the twine around the growing stem to support the plant in its growth towards the top. The twine needs to be tight enough to provide adequate support for the plant, and long enough to support the whole plant during the entire season. As the plants grow taller they‘ll be moved sideways, step-by-step, by either moving the bolt/hook, or by simply moving all the support twine one step sideways in the same direction.

Close but airy

Don’t space the plants too closely together in the greenhouse. It’s tempting to do so because the plants look quite tiny and spindly at the beginning, but it’s necessary to follow proper spacing to prevent introducing or spreading disease. Always plant in a triangular pattern—in zigzag formation—in order to provide each plant with as much space as possible. This is something to remember even when dealing with potted plants. It’s difficult to say just how much space is enough space between plants, but as a general guideline we use two to three tomato or cucumber plants, complete with access paths, per square meter (10.76 sq ft) of greenhouse surface. A 10 square meter (107.65 sq ft) greenhouse will hold approximately 25 big plants, in addition to a variety of potted plants. Grape vines and fruit trees need more room and thus will allow less space for other plant life.


Vertical cultivating. The twine starts off attached to the base of the plant.


It is easier to grow tomatoes than to start tomato plants from seed.

As the plants grow in height, you can plant lower-growing plants between them. Basil likes a lot of warmth and thrives in the greenhouse, especially between tomato and cucumber plants. While the plants grow, make sure to keep the soil below them clean and weed free. Even if there are other plants in between them, you’ll need to keep the ground neat. Don’t leave the weeds and clippings on the ground—they belong in the compost pile.


Many plants that grow in the greenhouse will need to be pruned. Not all shoots should be allowed to grow, as otherwise the greenhouse would turn into a dense, shadowy jungle where the plants would get insufficient light and space. Inferior and smaller fruits would hardly ripen, and plants might also abort their fruit—i.e., spontaneously shed their unripe fruit. Plants need sun and air to produce a good crop. (Each growing tip includes a proper pruning how-to related to the plant subject.)

Wilted and diseased leaves are cut off and thrown away. It’s preferable that the leaves be kept off the ground to prevent the growth of grey mold. Leaves resting on the ground are cut off at the mere hint of trouble, so in the end the plant’s bottom segment might look a little bare, but its upper part will be healthy and green. Most important is to make sure that the leaves at the top get plenty of light, as the bottom leaves quickly become spent and can subsequently be removed without a second thought.

Do more companion planting

Even if you only buy plants, you might be lucky and happen upon several different varieties meant specifically for greenhouse growing. Take care to label your pots. Chili peppers come in different strengths; bell peppers in many beautiful colors; cucumbers vary in length; tomatoes might taste more or less sweet, even slightly tart, and they also vary widely in size and color. It isn’t more challenging to grow several varieties, and it won’t affect the quality of your harvest. It’s perfectly fine to grow tomato and cucumber plants in the same greenhouse; just don’t store their fruit together in the refrigerator.


Growing tomatoes in the greenhouse is both rewarding and easy. They do take a while to ripen, so if you’d like to enjoy tomatoes over the summer it’s best to start the plants early. They can be started from seed indoors, or can be bought ready for transplanting at a nursery; the challenge lies principally in starting a tomato plant from scratch and not so much in growing the tomato itself. The advantage of starting the plant from seed is that you can select any type of plant you want; however, plants that you buy at a garden center are often of better quality than those started from seed at home, since they’ve been exposed to more light and the plant is more compact. Problems can arise in transporting the plant from the cultivator to the point of sale, which can stress the plants and make them not feel and look their best. They’re also accustomed to the carefully maintained environment of a professional greenhouse, so they might have a rough time acclimatizing to a colder hobby greenhouse, and thus might slow down their rate of growth—at least initially. The hobbyist’s own plants are already well used to less than ideal surroundings, and so have no reason to slow their growth in this manner.

From seed start to flowering stage, you can count seven to eight weeks under favorable conditions. Add another seven to eight weeks from bloom to ripe fruit. That adds up to almost four months, which means that if you want to eat tomatoes in July, you’ll need to start your seeds in February.


Tomatoes exist not just as different cultivars, but also in different types. Those that produce really small-sized fruit usually grow clusters containing lots of fruit. The bigger the tomato, the fewer tomatoes will be in the cluster. Mid-sized red varieties usually give the most fruit per kilo (around 2 lbs) weight per plant. The variety you choose to grow depends on your personal taste and preference, and flavors of tomatoes vary widely. Smaller tomatoes usually have a more pronounced, intense flavor, while big beefsteak, slicer-style tomatoes can be more subtle-tasting. It also depends on how they’ve being grown: plenty of sun and sparse (but not stingy) irrigation will help concentrate flavor in the fruit far better than if it’s kept in a shady spot with plenty of water.

Seeds for good quality tomatoes are pricy—some can cost as much as ten to twenty Swedish Crowns ($1.50 to $3) per seed—but a good quality fruit is easier to grow than a cheaper variety. Good quality tomatoes also exhibit superior resistance to different diseases, and can tolerate vagaries in the weather without halting their growth. Seeds for many of the rare and quirkier kinds of fruit, such as the ancient heirloom varieties yielding black, green, stripy, pink, yellow and white fruits, are also available for sale on the market. These are often more unusual rather than of reputable quality, and expensive merely due to their rarity. The easiest fruit to cultivate are the red, regular-sized cultivars, quite simply because breeding programs have concentrated on producing this kind of uniform and reliable fruit. Also, as a rule, newer varieties tend to be more disease resistant. Nevertheless, it’s always a good idea to grow several varieties of tomatoes for different uses: the common red greenhouse tomato for salads, a smaller variety to pick and eat straight from the plant, a yellow variety for its lovely color, and a tempting new cultivar. Grown together, they all make for a nice healthy mix.


It’s your choice: Start tomatoes from seed or buy young plants.


A tomato plant is planted in a large pot, in a bag, or in the ground. It’s trained to grow towards the ceiling as described earlier, on page 62. When flowers start to appear, give the plants a slight shake, or give them a quick shower, every day. Tomatoes are self-pollinating, but the pollen needs to fall onto the pistil for pollination to take place. When the plant is shaken or watered, the pollen loosens and then undertakes self-pollination. You need to water the plant daily—and drip irrigation is almost always a must. If you have not set up a drip irrigation system, you’ll need to water the plant every morning, midday and early afternoon (but do not shower the plants in the evening, as this will gives disease an opportunity to set in). Count on giving a large tomato plant several liters (several quarts) of water each day. Do not use a hose or spray attachment when watering, as the water is too cold for the plant. Instead, collect water in drums and watering cans after the watering is done, then leave them in the greenhouse until next watering. During that time the water will have time to reach a more gentle, lukewarm temperature.


The tomato plants are only transplanted into the ground when the soil is warm enough.

Tomatoes prefer ambient temperatures around 20ºC to 25ºC (68ºF to 77ºF). Ventilate the surrounding air properly to keep the temperature constant and not too hot; an automatic roof ventilation system is very helpful (see page 146). Another way is to shower the floor to lower the temperature and raise the air’s moisture content.

Remove sucker shoots and clean the tomato plant each week. Most greenhouse tomatoes are indeterminate, which means that they can reach dizzying heights. They grow sucker shoots in the joint where lateral stem meets the main stem, but they must be removed—these small shoots are called ‘suckers’ because they suck away nourishment and energy needed for the main plant. There might be shoots all the way down at the foot of the plant and they have to be removed as well. Even though the shoots are removed, you can be certain there will new ones the following week. Sucker removal is a chore that needs to be taken care of on a weekly basis, as there will always be new shoots sprouting, week after week. Everything wilted and dry must also be cleared away. The lower leaves will turn yellow after a while—cut off the most wilted ones, approximately three leaves per week—but don’t remove all bedraggled-looking leaves, as the plant needs green, working leaves in order to set fruit. Broken shoots, leaves and other damaged parts need to be removed. Keep winding the twine once around the plant’s main stem each week (see page 62). Avoid wrapping leaves and flower clusters under the twine, as this can cause them to break off. The plant can be moved slightly to one side once it reaches the ceiling. The lower part of the plant—which will most likely be bare of leaves at this point—will lean away from its planting spot on the ground. If the plants are left to grow long enough, they will eventually ‘walk’ sideways around the greenhouse, like in next page’s picture.


Shake or shower the plant so it can perform self-pollination.

The tomato plant can continue to grow in this manner, with its uppermost segment always in the light, and continue to produce new flowers and fruit over a prolonged time period. If you’d rather not have such a big, tall plant, just top it off (in other words: cut the top off) when it reaches the ceiling. This will effectively stop any further setting of flowers.

Top off the plant once the summer comes to a close. As it takes about two months from flower to harvest, you can predict the approximate date at which you can do this, and which you’ll need to do in order to divert the plant’s energy into ripening its already existing green tomatoes.


When the plant reaches the ceiling, its top is moved sideways. This makes the plant lean.

Certain varieties such as the so-called bush tomatoes only grow to a height of about 1 m (3 1/4’). No shoots are removed and they are not pruned at all as they are grown as bushes. All shoots growing in the axil where lateral stem meets main stem are left intact on these plants. The same applies to hanging tomato plants, as well as miniature varieties for hanging baskets and window/balcony boxes. These tomatoes grow very little so they’re allowed to keep all their shoots. The seed packet should explain whether the tomato plant is the kind that needs sucker removal and pruning, or not.

The harvest

Check on the plant regularly, even if its irrigation and feeding are set up to take place automatically. Make sure it sets fruit, as each flower is a potential tomato in the making—big or small. Cherry tomatoes set many flowers so it’s not quite as important that every flower be pollinated. The bigger the tomato, the fewer the flowers in the cluster, which means that it’s much more important that they’re all fruiting. The tomato starts out as a small, unripe, green fruit that grows and increases in size slowly. Usually, the tomatoes ripen one by one in the bunch, and they are harvested a few at a time. For grape tomatoes, the cluster is left intact until all fruits ripen and the bunch becomes very heavy. At times you may have to use special plastic supports that you attach to the stem. You can often buy them at greenhouse supply stores and at seed firms catering to professional growers.


Remove sucker shoots from the joint between lateral stem and main stem.

Pick your tomatoes regularly. If there are too many tomatoes on the vine at any time, it’s better to pick them and keep them in the refrigerator than to leave ripe red ones on the plant. If the ripe fruit is left on the plant, then the plant will set flowers very sparingly, which in turn will make it produce less fruit in the long term.

Tomatoes can be frozen directly after picking, without blanching or cooking. Place them in a freezer plastic bag and, if you wish, add a few sprigs of fresh herbs (such as oregano and basil) to it. When you want to use the tomatoes, just add the herbs to them when you cook a sauce or a stew.

When the weather turns cold and it’s time to empty the greenhouse, there will still be a lot of green unripe tomatoes left on the plants. Harvest them, either one by one or by bunches, leaving the blossom end and a piece of the stem intact, then let them ripen in a sunny spot in the house, or cook them while they’re still green. To delay the ripening, and save the tomatoes as long as possible, store them in a cool place such as a pantry or root cellar.


The greenhouse with loads of tomatoes at the height of summer. They ripen from the bottom up.

An array of tomato sizes

Cherry tomatoes: 10, 25, and 30 gr (1/2 oz., slightly under 1 oz., and slightly over 1 oz.)

Plum tomatoes—larger and more elongated than cherry tomatoes: 30 to 50 gr (1 oz. to just under 2 oz.)

Mid-sized tomatoes: 60 to 100 gr (just over 2 oz. to 3 1/2 oz.)

Beefsteak tomatoes: a hefty 200 gr (around 7 oz.)



On the whole, growing tomatoes is easy: there are a few pests to contend with, but no major obstacles to overcome. There will always be some damaged and ruined fruit, especially during the fall. Much of the common damage is caused neither by disease, pests, or insecticide treatment.

Split fruit is usually caused by uneven irrigation and/or a sudden shift in temperature—a really hot August day followed by a chilly night, for instance. Split fruits is a common sight in the fall.

Curling at the edge of plant leaves is also caused by too large a temperature swing between night and day.

Leaf discoloration and yellowing tops are signs of nutrient deficiency, and which can be remedied by adding liquid fertilizer to the irrigation water. Even with automatic irrigation, it might be necessary to add extra nutrients to the water when plants are at their most productive.

Yellowing leaves at the bottom of the plant is a sign of natural aging. Simply snip them off, a few at a time.

If the plant sets no fruit even when there are flowers, the cause might be a lack of pollination. You’ll need to jiggle, shake or shower the plant with a spray of water to help the pollen drop and reach the pistil. A beehive can be bought and placed in the greenhouse to promote pollination—they can be purchased from companies specializing in organic horticulture.

Lack of fruit can also be a sign of an overheated greenhouse. This is a very common problem. Tomatoes don’t like temperatures above 25ºC (77ºF), and at 28ºC to 30ºC (82.4ºF to 86ºF) the flowers can no longer produce any fruit. Make sure to keep the greenhouse ventilated during the day, and leave doors and windows open if the greenhouse is going to be left without supervision over a few days during the summer. Refer to the part about ventilation on page 146.

Plants and fruit can be damaged by cold and frost during the fall. When clear or ‘greasy’ looking spots appear on the fruit, it’s usually due to cold or frost damage. The green unripe fruit seems firm and unblemished but becomes soft and mushy when ripe.


The tomato’s main tormentors are usually aphids and white flies. Swedish cultivators use organic, eco-friendly treatments consisting of beneficial insects to combat pests, instead of using chemical insecticides. Organic methods work in hobby greenhouses, but they require constant temperature control. It can also get rather expensive for a hobby grower to buy these natural ‘predators’, but if you’re interested in this method, refer to page 184 for suggested reading on this particular topic.

Black soot on the fruit flags a problem caused by aphids. The sticky (‘honey dew’) substance on leaves and on fruit is the telltale sign of an aphid infestation. A sooty fungus grows in the sticky substance, and while it’s unsightly it is not dangerous, so just wash it off before eating the tomato. You can rid the plant of an aphid infestation by spraying it and the fruit with water, especially on the underside of the leaves. Plant sprays can also be used in several rounds, according to packet instructions.

Whiteflies, small and white, are also a form of aphid and they can be found on the leaves’ underside. They can also cause Black soot. Spray with water and perhaps an organic pesticide. Unfortunately, whiteflies are difficult to get rid of—they move very quickly and the organic pesticide has to hit the whitefly directly in order to be effective.

Vegetable hornworms eat big holes in leaves and sometimes even in the fruit. They’re difficult to get rid of, as they are busy movers. Pick off the visible ones, give the plants an early morning shake, then remove and destroy the larvae that fall to the ground.

Slugs make big holes, too. The difference here is that they secrete and leave a slimy, shiny trail behind them. Sneak into the greenhouse in the evening and try to collect them. You can also spread special slug bait that is harmless to other animals and to humans. This needs to be done at even intervals.

Holly leaf miner leaves behind long narrow winding trails. If there are only a few leaves that have been affected, simply remove and burn them; if the damage is more substantial there is nothing that can be done. You can stop an attack if you discover it early on, and if you remove the leaves at once. Still, the harvest will be smaller as some leaves have been destroyed.

Fungal diseases

Leaf mold is a common problem during late summer and fall. This disease is common in both tomatoes and potatoes. Leaves on tomato and potato plants turn brown and wither. Cut away the affected leaves as soon as they show up, and throw them in the garbage or burn them. Don’t grow potatoes beside or inside the greenhouse, and opt for varieties that are disease resistant—this will be highlighted on the seed package. Older tomato varieties featuring more potato-like leaves are more prone to this type of attack.

Blossom-end rot is a fungus that attacks the fruit. Tomatoes develop large dark spots that are firm at first, but then soften. The only thing to do is throw away the tomatoes that have been attacked. Blossom-end rot is common among fruits in the fall.

Grey mold is also a late summer problem. The leaves turn brown and are covered in grey fuzz. Cut off the leaves as soon as you see them, and remove them from the greenhouse. Avoid touching any greenery with the diseased leaves to prevent the spread of the spores to the rest of the greenhouse. A way to mitigate this problem is to heat the greenhouse during the night—a fan heater is good—and provide proper ventilation during the day. Grey mold thrives when the days are warm but the nights are cold and humid—a natural occurrence in the fall. Don’t irrigate or shower the plants in the afternoon, as the humidity stays on during the night.

Powdery mildew is another common fungal disease. It coats the plant in a white powdery substance. Some tomato cultivars are more susceptible to it than others. It’s best to only grow disease-resistant varieties of tomatoes, because there isn’t much that can be done once the plant has been attacked. If the fungus is discovered early, remove the affected leaves and spray the plant with an organic plant treatment. Try repeatedly spraying it with a garlic spray, as it has shown to help against powdery mildew on cucumbers.


Bell peppers come in many colors.

Bell peppers and chili peppers

Bell peppers and chili peppers are fruits from the same plant. They’re both Spanish peppers, and have been crossbred to produce the large, juicy, sweet and meaty fruits called bell peppers and the smaller pungent fruits with thin walls—the chili peppers. There are several kinds of peppers with edible fruits, of which the chili pepper is the most common. Both bell and chili peppers thrive in sunshine—the sunnier it is, the tastier the fruits will be.

Bell and chili peppers can both be bought as plants, or can be sown as seed. It’s best to use commercial seeds when growing bell peppers, since the seeds in the bell pepper fruit from the vegetable bin at the grocery store rarely produce the same kind of fruit as the one that provided the seed; plus, it’s not clear how long it will take to grow the pepper in the Swedish climate. It’s better to buy a proven cultivar, either in a seed packet or as a plant, as that will guarantee the type that will grow to harvest in our climate. Chili peppers are a different story—it can feel a bit like an adventure to collect seeds from store-bought fruit. Just keep in mind that the resulting fruit will not be exact copies of the original, and that the fruits will in all likelihood not taste the same. Seeds from fruits grown in Mexico but sold in Sweden will not grow into the same strong-tasting specimens.


Bell peppers and chili peppers can be grown in pots. Many varieties sold as seeds don’t grow into large plants even if the fruits are large. You can grow them the same way as tomatoes, trained vertically with twine, and pruned heavily. Another way is to grow them wide and bushy in large pots. The large bush needs support in the form of a sturdy wooden stake—bell peppers especially, since the fruits can get heavy enough to break their stems. If the plant is grown as a bush, you won’t need to remove any of the shoots.

Shape the trained plant by cutting off most of the shoots that sprout, and save one shoot to be trained vertically. Wrap the twine around the plant close to its planting spot, and fasten the twine to a hook or bolt in the ceiling. Remove the new shoots that appear at the top to keep only one main shoot. Two shoots often appear at the same time, so with time the plant gets a staggered look. You can also save two shoots further down on the plant—tie them to their separate pieces of twine, then lead those out from the plant and fasten them to the ceiling, which will give the plant the appearance of a Y. It’s not as cumbersome as it sounds—the main thing is that the plant flowers and sets fruit, and that the sun gets a chance to shine on the plant.


Bell and chili peppers can be harvested both ripe and unripe. Depending on the variety, unripe ones start off green then ripen to yellow, red, orange, or blackish brown. There are others that are red when unripe only to turn into a brownish black color. The seed packet should provide this information so that it’s clear when the time has come to harvest the fruit. There can be significant differences among the different varieties. While large fruits generally have a mild taste and smaller ones are stronger, this doesn’t always hold true. There has been so much cross breeding that some fruits are reminiscent of tomatoes, while others are searing hot. The heat strength of the fruit should be labeled on the seed packet. Most commonly, unripe fruits are milder tasting than ripe ones.

While the fruit is ripening and still attached to the plant, flower production slows down. You’ll have a bigger harvest—i.e., more bell and chili peppers per plant—if the fruit is picked unripe. Snip off the fruit, leaving a piece of the stem attached. If the stem is removed, it leaves a hole in the fruit that can start to rot, shrivel up, or go moldy. Bell peppers can be harvested a few at a time and frozen. They are not good candidates for ripening inside, as the fruit will shrivel up.


Ripe, burning hot red pepper.

Harvesting pepper fruits requires extra caution, because the fruit can be very hot, so if you touch your face or rub your eyes after holding a pepper, it might make your face and/or eyes burn for quite a while. Peppers don’t ripen once they’re picked, but they can be dried; leave them sitting longer on the plant, then dry them in a sunny spot with good air circulation. You can also thread the peppers on a coarse thread and hang them out in the sun to dry. Do not leave the peppers in a pile, or they risk going moldy.


Yellowing leaves can plague both bell and chili pepper plants. The reason might be that they have dried out too much, or that they suffer from a lack of nitrogen. Try adding liquid fertilizer to the irrigation, then check to see if new emerging shoots are green. The leaves can also turn yellow or lilac, or show yellow spotting when nighttime temperatures dip, which is something these plants don’t like at all. Unripe fruit that falls off the plant can be a sign that it lacks water and/or nutrients (as there are often many fruits developing at the same time) so make sure the plant receives weak fertilizer each time it is watered.

If you see brown, spotty, shriveled, and malformed fruits, or notice that some fruits don’t grow as well as others, you can always remove them from the plant since it’s counterproductive to make the plant expend energy on developing fruits that are going to end up being inferior to the rest. However, fruits that are merely disfigured due to an insect’s bite or sting taste just as good as unblemished fruit, so they can be put to use in a salad or hidden in some other dish.


Both bell and chili peppers suffer from frequent infestations of aphids and whiteflies, which are a form of lice that spread rapidly and are extremely frustrating to deal with. To make the task of keeping the infestation under control a little easier, place the plants outside when it’s warm and shower them. While it’s practically impossible to eradicate all the aphids and whiteflies, you can spray the plant with organic insecticides—but not under direct sun, as this will cause the leaves to burn. The advantage of growing plants in pots is that the affected plant can be moved out of the greenhouse, thus ensuring that the other plants in the greenhouse are not affected to the same degree. Check the underside of leaves often to catch when the onslaught begins (the emphasis here is not on if, but on when), as it will be easier to treat the problem successfully the sooner it’s discovered.

Spider mites will occasionally attack bell and chili peppers. They show up as teeny tiny yellow spots on the leaves (see the example of a cucumber plant, page 76).

Slugs will eat the leaves, so spread special slug bait, then pick up and dispose of all signs of slugs.

Fungal diseases

Grey mold and other fungal diseases can show up in late summer and in the fall. Remove shriveled, brown leaves with greyish fuzz as soon as they appear; be careful not to shake them around in the greenhouse, and wash your hands and the tools used to remove the grey mold, because grey mold spores are small and spread easily. Leaves should be dug down in the compost pile or thrown directly in the trash bin.


The eggplant flower illustrates that the plant is a close relative of the potato.


The eggplant is also a relative of the tomato and thus likes warmth and sun. If it hasn’t been started in the greenhouse in the spring, it will not have adequate time to produce a crop. When the summer warms up it can be placed outside, just like bell and chili peppers, but it does need a longer stretch of summer climate than is typical for Sweden. Eggplants can be trained to grow vertically with the help of twine, but most common varieties are low and bushy. They produce fruits that are slightly smaller in size than the dark purple, pound-sized fruits we find in the vegetable aisle at the grocery store. The fruits come in white, lilac, green or stripes, they are oblong or round, or small and fingerlike. The smaller, finger-like type is favored in Asia, while Southern Europe is partial to the rounder, purple variety.

If you want to grow your preferred kind of eggplant, you’ll have to start the plants from seed. Eggplant seeds are not a common sight in garden centers, although they do exist. Buy your seed in packets—do not attempt to use seeds from fruits. Also, seeds bought during a holiday trip to a warmer climate will require a far longer and warmer summer than we typically have in order to produce food that is edible; you will have far better success if you purchase your seed from Swedish producers that carry seeds best suited to Sweden’s northern climate.


Sow each seed early and in its own pot, and place them in a spot with plenty of light. They need 25ºC to 30ºC (77ºF to 86ºF) to germinate, and require a long growth period inside. Pot them up into larger containers several times, and don’t move them into the greenhouse until it’s warm in there both day and night—these plants demand high soil temperature. Use some caution while irrigating the plants during the seedling stage—let the soil dry out slightly between waterings.

Later, place the plant—whether seeded or bought—in a large pot and fertilize regularly. If the plant is to be trained vertically, remove all the shoots except for one or two, and attach them with twine to hooks or eyebolts in the ceiling structure. The twine follows the plant and is looped around it as it continues to grow.

When the plant starts to flower, help it along by patting it softly inside the flower with a small watercolor paintbrush to ensure that pollination occurs. This might not be entirely necessary, but do it anyway—better to be safe than sorry. If you want to grow your plant into a bush-like shape, top five or six leaves to make it branch out well.


Eggplants will fruit without pollination, but require warm days—preferably around 25ºC (77ºF)—and cooler nights, for this to take place. Pick the fruits as they ripen and are of the right size and color. The quickest fruit to grow are the small varieties that have their origins in Asia. Don’t leave the fruits on the plants longer than necessary—pick them and store them in the refrigerator instead. The eggplant will not ripen after being picked, and should either be used directly or stored in a cool place.


Yellow or discolored leaves may be caused by chilly nights, since eggplants need warmth to thrive.

Plants that refuse to grow are probably in soil that’s too low in temperature—they will stop growing completely if placed in cold soil. Low soil temperature and/or lack of nutrients will also cause the plant to shed its fruit.


Eggplants can have white, green, or lilac skins, and come in different sizes.


Aphids and whiteflies are common problems. The leaves of the eggplant are slightly fuzzy, which makes for a comfortable, protected space for the aphids, and by the same token makes it challenging to dislodge them by showering the plant—which is more easily done on the bell and chili peppers’ shiny, slick leaves. Check the underside of the eggplant leaves at even intervals to try and spot the aphids as early as possible. Shower the plants with water and spray with organic pest control as needed. Move heavily infested plants outside, away from the rest of the plants.

Spider mites produce light spots on the slightly fuzzy leaves of eggplant. It’s a pretty common problem (see an example on a cucumber on page 76).

Fungal diseases

Eggplant risks being affected by grey mold if the atmosphere turns cold and damp. There’s no remedy except proper ventilation in the greenhouse during the day, and the use of a fan heater during the night.

If the plants have been kept outside during part of the summer they will need to move into the greenhouse at night once the evenings turn chilly and damp again.

Pepino (Solanum muricatum)

A pepino looks similar to an eggplant. It has a bush-like growing habit with many branches. Its flowers shift from white to blue violet, and after a while it produces oval greenish-white fruits with stripes in brownish lilac. The plants grow very rapidly and require heavy fertilizing to bloom and produce fruit, but the plant itself doesn’t grow taller than approximately one meter (3’ 1/4).

You can buy pepino seeds, but it’s more common to buy the plant itself. You’ll seldom find more than one variety of pepino in Sweden, as this is an unusual vegetable for the country—both in seed and plant form. Pepino is grown like an eggplant, is an excellent potted plant for the greenhouse, and needs warmth to thrive. The fruits grow fast after pollination; they have a sweet melon-like taste and are eaten fresh without any special preparation.


Cucumbers are as easy to grow as tomatoes. Cucumber plants yield more quickly; there is less wait time between sowing and harvesting. Small cucumbers are sweet and tasty even if they’re picked a bit too early, while early unripe tomatoes are not tempting. Cucumbers require more heat than tomatoes, and are even more chill sensitive.

It’s easy to start cucumber plants, but the cost of quality seeds can be steep. A seed packet will often contain only five seeds, and among those only four will germinate. For this reason, each seed deserves its own container. Make sure to choose a variety of garden cucumber especially bred for greenhouse cultivation. A combination of parthenocarpic and gynoecious varieties is best, as they contain mostly female flowers that require no pollination; these are also good if you want to avoid pesky cucumber seeds. There are traditional, long cucumbers, as well as newer, shorter varieties—the greenhouse mini cucumbers. Both are smooth skinned and dark green. Powdery mildew affects cucumbers easily, so make sure that the varieties you choose are powdery mildew resistant. This information should be printed on the seed packet.

Cucumber plants age much quicker than tomato plants, so it’s a good idea to save a few seeds for planting later on in the season. Depending on where you live and the date for first frost for the area, it might be worth the effort to put a few new sturdy plants in the greenhouse in July. Sow directly into pots and place them in the greenhouse, ready at hand when needed.


The temperature needs to reach 25ºC to 28ºC (77ºF to 82.5ºF) in order for cucumber seeds to germinate. Place the seeded pots on a tray on a windowsill above a radiator. Cucumbers don’t transplant gladly from flat to pot, so it’s better to direct sow one seed into each pot. After a few weeks the plant will be big enough to be safely moved into the greenhouse. Don’t make this move too early, however, as the cucumber won’t tolerate below 15ºC (59ºF) temperature during the night. If it’s too cold, the plant can stop growing and will simply turn yellow. Store-bought cucumber plants will often stop growing momentarily when they are moved from a well-heated commercial space to a hobby greenhouse, but after a few weeks they usually begin to grow again. The plant grown from seed at home should spend a few weeks in the greenhouse before being planted out.

Cucumbers grow quickly in a warm environment, so the timeframe from sowing to harvest depends mostly on the weather. It can happen quickly if there is a heat wave at onset of June. If spring is cold, however, the plants may sulk and nothing may happen for several weeks. That’s why growing times can’t ever be exact—there can only be approximations. Once the plant starts to grow, it can develop 10 cm (4”) in a single day, so you’ll need to work fast to get the plant in the ground, train it and tie it up before it gets so long that it breaks.

If you’re growing cucumbers in large containers, place them on a bottom layer of soil in the reserved pots and fill with warm soil, not with soil from bags (which can be too cool). If the plant is to go directly in the ground, don’t dig a deep hole. Simply place it on the broken surface and then fill the hole and surround it with store-bought soil. It will end up looking somewhat like a small hillock. It’s probably still a bit cold in the ground even though the surface may be warm; you can measure the soil’s temperature with a special thermometer before planting the cucumbers to make sure that it’s at the desired temperature—about 15ºC (59ºF).

Cucumber plants have frail roots and delicate stems. The roots don’t have the strength to draw up enough water to sustain the whole plant. It’s not unusual to see plants droop during the hottest part of the day. Left in this condition, neither plants nor fruit will grow, so shower the plants several times a day when the weather is warm and sunny. If you haven’t set up a drip irrigation system, you’ll need to water the plants several times a day, avoiding late afternoons and evenings—humidity and dampness late in the day increases the risk of the plant developing grey mold.

Pinching and pruning

A thriving cucumber grows almost like a weed. Small shoots and budding, immature fruit grow together at the leaf axils. Pinch off the shoots without damaging the immature fruit. Each budding fruit consists of a small yellow flower attached to a swollen ‘body’ that will eventually develop into a cucumber.

Cucumbers are trained with twine attached to the ceiling, just like tomatoes (see pages 62 and 66), and are moved sideways in the same manner when they reach the ceiling. Another method is to pinch off the top, and leave two shoots in the leaf axil to develop into two new tops that are allowed to hang, or grow downwards. Depending on individual preference and available space, the new tops can also be allowed to grow sideways along the ceiling.

Alternatively, you can save a shoot from the plant early on and train it sideways. This will make the plant form a big Y with two lengths of twine from the base of the stem and up to the ceiling. That way, two cucumber plants will grow from one quality plant (if they’re expensive), or if one has broken off, wilted or has died down.

The best way to heal a damaged stem is to dab some soil on the wound. Wilted, yellowing leaves are of no use, and should be cut off.


Flower and immature cucumber show clearly here. Small shoots that need to be pinched off grow in the same space.


Showering the plants reduces the risk of spider mites.


Cucumbers grow from the plant stem and need to hang unobstructed—immature fruit can’t be trapped in the supporting twine. The first cucumbers will appear at the bottom of the plant and then progressively higher up. It’s important to keep pinching the top to encourage the plant to grow, to produce more leaves and new fruit in the axils. Cucumbers can be harvested at any stage, even when they are tiny; the little ones are delicious, but harvesting early means that the yield in kg (lbs) per plant will be lower than if the fruit were left to ripen longer. The best time to pick them is when the fruits are the size of commercially sold cucumbers.

Don’t let cucumbers grow too large, and don’t leave them sitting on the plant. Extra large cucumbers are not the mark of a master gardener—quite the contrary: large, pale green cucumbers are not tasty, and they hinder the plant from setting new fruit. A cucumber with only one swollen end should be harvested immediately, as it has only been partially pollinated and will never improve. You should eat it, however, as it’s delicious while still small. It’s not uncommon for a plant to set more immature fruit than will reach full maturity. If there are yellowing or withered immature fruits, remove them to leave the plant more energy for the remaining maturing cucumbers.


Immature fruit, and a soon ready-to-harvest cucumber.


Many problems suffered by cucumbers are caused by lack of heat. Yellowing plants, plants that stop growing—these are examples of problems that are caused by chilly nights. Leaves that turn yellow while the plant is still young is yet another cold environment issue, and might be the reason for yellowing fruit that drops off the plant. When plants won’t grow, cold is usually the culprit. Irrigation and fertilizing is highly important, as yellowing leaves and falling fruit might also be caused by lack of nutrients and water.


Spider mites (also simply called mites) are cucumbers’ biggest enemy. At first, the leaves show yellow spots before turning dusty grey, after which they wilt and die. The whole plant is affected—it becomes weak and yields little, as it depends on green leaves for energy to continue to grow. Treat it by showering the plant inside the greenhouse during the middle of the day, when the atmosphere is at its warmest and driest. Automatic fogging or misting (see page 167) is a good solution. Remove all yellow leaves immediately, and spray regularly with organic, non-toxic plant treatments. Swap out your severely mite-bitten plants for new, healthy ones. Clean the greenhouse thoroughly each fall, as spider mites will often overwinter in the greenhouse, and are ready to infect new young plants in the spring.


Growing cucumber plants. They don’t take long to go from flower to mature and ready to pick.

Aphids like cucumbers, but they too can be fought with organic treatments. Cucumber leaves are slightly sticky, which gives aphids a good grip and protection, so make sure to spray the underside of the leaves extra carefully. Irregularly formed cucumbers can be the result of an infestation of the tarnished plant bug (lygus lineolaris). This pest injects the fruit with a poison that terminates all growth in that spot, which usually causes some malformation in the fruit. The fruits are perfectly all right to pick, as they are still edible—their growth pattern has changed but they are neither poisonous nor dangerous.

Fungal diseases

Powdery mildew can attack cucumbers. Entire leaves can look as though they’ve been dipped in a milky liquid; sometimes it’s white and powdery. Buy only disease resistant plant varieties, and maybe spray with organic, nontoxic plant treatments, or treatments containing garlic extract. Weed meticulously between the plants and remove all plant leaves that touch the soil.

Gummy stem blight rots the narrow end of the cucumber. Be extra careful to keep the soil area clean around the plants, and clean by removing all plant debris and affected parts. Air out the greenhouse during the day to prevent high levels of nighttime humidity.

Grey mold makes cucumbers turn brown, tapering off to grey fuzz. Leaves and stems can also be affected. It’s easy to recognize the grey fuzz, as it also regularly appears on strawberries. If the plant is young, you can try to remove the infected part as part of the cure, and then patch the bare spot with soil. If the attack occurs during late summer or fall, you may as well remove the affected part and hope for the best. Cold, wet nights are the culprit, and the way to combat this is, again, to air out the greenhouse properly during the day and use a fan heater during the night to prevent moisture build-up.


Melons look a lot like cucumbers, but they usually only yield a few fruits per plant, as they are so much larger. Our selection of melon types is rather slim in seed packets, because Sweden is just a tad too chilly for them, and they almost always need to be grown in a greenhouse. We do have a smaller muskmelon variety, Aroma, that has been melon growers’ to-go fruit for many years. ‘Sweetheart’ is also easy to grow, is self-pollinating, and produces many small fruits. Varieties offered by foreign seed companies can be problematic to grow here, as they usually require much more warmth over a much longer time span than Sweden has to offer. A truncated growing season will bear melons that lack their characteristic sweetness and taste. You may succeed, however, if the summer is warm and sunny.


Melons are sown and cared for in the same manner as cucumbers. It’ll take between four and six weeks between sowing and transplanting them to the greenhouse. Melons can be grown in-ground or in large containers; they need very warm soil—nothing below 20ºC (68ºF). The plants are trained in the same way as cucumbers, with the help of twine that is fastened to the ceiling. The twine is attached around the plant stem at soil level, but the fruits will require added support: each individual fruit needs to be supported separately by mesh bags (or netting) that are fastened to eyebolts attached to the greenhouse structure. If not, the heavy fruit will dislodge the whole plant; if the plant tumbles to the ground the stem will break, and the fruit will burst. The string might also break. Raffia ribbon is not strong enough here, so use plastic covered parcel string instead.

Pinching and pruning

Melons are pruned according to cultivar. Slow-growing varieties with closely spaced leaves are topped over three leaves, leaving two shoots to grow towards the ceiling, just like the cucumber plants. The old variety called ‘west’ (which is still sold in the garden centers) is such a melon. The sturdier and faster growing varieties, with wider spacing between leaves, are trained while the tops are left intact.

Pinch off the side shoots that appear in the leaf axils and are missing female flowers. Side shoots with female flowers are removed one leaf from the flower/fruit. If additional shoots appear on the new leaves’ axils, repeat by removing shoots outside one leaf (this may seem like a bit of a chore, but it really isn’t labor-intensive). What remains is a trained vine that reaches the ceiling. A shoot with an immature fruit should stay in each leaf axil, or no shoot at all. Any excess shoots with immature fruit are removed, as each plant can only support so many fruits.


In order to ensure a decent harvest, melons need help with pollination. Pollinate several flowers in one go while they’re in bloom. If they are all pollinated at the same time, they will grow evenly and will likely be of similar size. (If the pollination is out of sync, the first ripe melons might become much larger, to the detriment of the later ones.) Use a small make-up or watercolor brush; start by dipping the brush carefully in the male flower, then pat the collected pollen on to the female flower. The female flower is the one with a ‘rounder’ profile, due to a slight swelling below the petal tube. For successful pollination, the ambient temperature must be above 18ºC (64.5ºF), and the best time to do this is before midday.

You can leave two or three melons on a vine to grow and ripen. Other immature fruit should be removed, but it will totally depend on the variety of the fruit. Its size can reach 1/2 to 2 kg (1 to 4.5 lbs). The description on the seed packet should state what kind of melon it is and how large the fruits are expected to grow. If all the fruits are left on the vine to mature, it will yield many melons but the fruit will be small. Let the melon grow over the summer, and make sure it gets plenty of water and nutrients.


Watermelon is not of the same species as our most familiar melons, and it is a different plant. Its fruits are much larger and heavier - between 1.5 and 3 kg (3 and 7 lbs). They are suitable for growing lying prone on the ground.

There is a slightly smaller watermelon variety, ‘sugar baby,’ which has yellow flesh. It’s well worth trying to grow, as it doesn’t reach the size of the other, larger types. Place a stone, a piece of Masonite board or something similar under the fruit to protect it from the ground, otherwise the rind might rot if it’s in direct contact with the soil.

Melons, both the more familiar varieties as well as the watermelons, can also be grown in cold frames. As they require a relatively large space to grow compared to their fruit yield, it’s an efficient way to free up room in the greenhouse for other plantings. Start the plants in large pots in the greenhouse, and don’t transplant them into cold frames until the summer heat is truly upon you. Be particular in removing wilted and dead leaves and in making sure the plant environment is kept clean.


Melons should be harvested once the fruit is ripe. This means that they should smell like melons, and that a soft indentation can be made at the stem: put a thumb on each side of the stem and press lightly; there should be a slight ‘give’ on the surface (this sounds easier than it actually is, especially if you’re unused to performing this test.) The time it takes from pollination to ripe fruit is approximately twelve to fourteen weeks, depending on variety. The fruits can probably ripen a little more at room temperature once they’ve been picked, but they should not be harvested if they’re too unripe. Remove all yellowed and misshapen fruit from the vine immediately, as they will never improve and are only siphoning away nutrients from the good ripening fruit.


Melons yield few but large fruits. The heavy fruit needs individual mesh or net support.


Melons experience the same problems as their close relative the cucumber—they’re both very sensitive to chill and high humidity during the nighttime. Most of their issues stem from too low temperature, but melons are even more sensitive to cold than cucumbers, plus they require pollination. The absence of fruit might be caused by non-pollination, as female flowers need temperatures of at least 18ºC (64.5ºF) for pollination to take place. If there are only male flowers on the vine, then female flowers have failed to form due to the cold.


Spider mites are a problem for melons. Their leaves become spotty, dry up, and drop (see the example of a cucumber, on page 76).

Slugs favor damp leaves that grow close together. They chew large holes in the leaves and can move high up into the plants. Trails of glistening slime are their giveaway, so search for them in the morning and evening damp, and get rid of them—this is especially important if the plants are trailing on the ground. Make a slug trap from an upside-down pot containing a potato sliced in half; reset the trap regularly. A beer trap placed among the leaves is another effective slug bait. Occasionally during hot summer days, larger animals such as frogs, hedgehogs, and cats seek out the cool and the shade that the lush greenery provides along the ground, but they won’t damage anything and are not harmed by slug bait.

Fungal diseases

The many leaves and their close proximity to each other makes for plenty of humidity around the plants. Since they’re extremely sensitive to drought and have frail root systems, you’ll need to water them often. This, however, makes for an ideal environment in which grey mold can move in and feel right at home. Remove the parts of the plant affected by this mold, and keep the area clean and airy by not setting the plants too closely to each other, and by avoiding irrigating them in the evenings. Another possible solution to this issue is to preemptively spray the plants with organic, nontoxic anti-fungal protection.


Ground cherry looks a lot like Japanese Lanterns. They have the same husk, but in different colors.

Cape gooseberry, ground cherry, and tomatillo

Cape gooseberry, ground cherry and tomatillo are all from the genus physalis and are close relatives of the garden plant bladder cherry—also known as ‘Japanese lantern’. All of them bear fruits covered by a paper-like husk. The Japanese lantern husk is large and beautifully colored in orange, but the fruit itself is small. Ground cherry and cape gooseberry have larger fruit and their papery husk is a simple, plain brown protection. Ground cherry and cape gooseberry are very similar, and their sweet-sour taste is akin to that of the tomato. These berries can often be found in the produce section of the grocery store, packaged in small clamshell containers, but they’re also very easy to grow at home.

The tomatillo is a pale green-white fruit that fills its papery husk until it outgrows the husk and bursts out of it. The fruit itself is as large as a plum tomato, but remains light green as it ripens. One of its most common uses is in salsa verde, a condiment typical of Mexican cooking. The tomatillo tastes like a blend of kiwi fruit, melon and tomato. Cape gooseberry and ground cherry are easily found at the grocery store, and are available as plants or as seeds for starting your own plants, although there’s usually little variety to pick from. Tomatillo is less common in Sweden and is not easy to find as a plant, so you will need to grow it from seed.


Ground cherry with its papery husk.


Ground cherry, cape gooseberry and tomatillo are simple to grow, but they need a long summer. It’s advisable to start them out in the greenhouse before moving the plants outside during high summer. Bought or seed-started plants can be planted in large pots or in-ground in the greenhouse, where they’ll grow into sturdy bushes that thrive in the sun and heat. Water regularly, fertilize, and keep the area clean around the plants. Once outside, they need to be in the sunshine with some protection from weather and wind.


The fruits are harvested one by one as they ripen—you’ll need to taste a few to determine if they’re ready to pick. Cape gooseberry and ground cherry should be a fairly intense shade of orange, and tomatillo will be light greenish white and have a slightly sweet taste; its husk will have split and curled away completely from the outgrown fruit. The fruits drop easily, so it’s best to harvest them often, or they’ll be lost on the ground. Cape gooseberry and ground cherry keep well and will continue to ripen after harvest—they can be stored for several weeks in a cool place. The larger tomatillo is not as good a keeper, but can still ripen a little after harvesting.


Tomatillos are attractive and very tasty. They look like ground cherry but are as large as golf balls.


Though all these plants are easy to grow, they can still develop yellowing leaves. The cold, a lack of nutrients or water can be culprits. These plants need a lot of sun and heat—a cold, rainy summer will make them unhappy and yield few fruits.


Whiteflies are always an issue around these kinds of thin-leaved plants that are irrigated frequently. Check both the tops and undersides of leaves regularly after an infestation. Organic pesticide can be useful after an attack; if the plants are in containers, move them out of the greenhouse before the pests can get to other plants.

Slugs can also be a problem. Collect the slugs and spread slug bait regularly.

Fungal diseases

Leaves can wither and be attacked by grey mold. Remove the affected leaves immediately and throw them in the garbage. Make sure the plants are spaced well enough apart from each other, as they grow close and grow many leaves. Remove wilted leaves, other plant debris, and keep the plant tidy.