Greenhouse Vegetable Gardening (2015)

Greenhouses are often wet on the inside, and they’re slow to dry; this near-constant humidity makes them the perfect environment for moss and mold to proliferate. If you bear this in mind, you can arrange your space like the inside of a workshop in order to minimize the dampness.

The floor

A beautiful stone floor will impart a nice homey feel, but if you want it perfectly level with the ground, you’ll have to excavate it a little before laying down the slabs (see Ground Covering, page 152).

Elegant brick flooring is expensive, in contrast to grey cement slabs, which can be had for next to nothing. There are many other stone materials to consider, too, so let your imagination and taste be your guide. Large, decorative plant-filled pots look nice on the floor.

You can also level off the soil and place pots directly on the ground, but that quickly gets messy and slippery. If you plan on cultivating in the ground, place stone slabs only to make a pathway between the plants as well as for an optional seating area.

Another simple trick is to remove some earth, lay down a thin layer of sand, and place stone slabs on top of it, although this can end up being a bit unsteady to walk on. The good thing about this option is that it’s easy and quick to try, and if the path isn’t well set down the first time, it can easily be redone.

Along the walls

Besides the floor, the interior of the greenhouse is comprised of shelving, worktables or benches, and a cozy seating area; there should also be storage space for bags, pots, flats, and miscellaneous gardening gear. If you’re not planning on using the greenhouse during the winter, it can double as a storage area for both plants and garden furniture.

Shelves for growing and training plants.

Many greenhouses on the market have interior fixtures attached directly to the structure; the shelving and workstation are screwed into the wall in different configurations. This is highly limiting, as you can’t, for example, set down heavy pots on an attached table without putting strain on the entire structure of the greenhouse. It’s better to use freestanding shelving systems and tables; they’re far simpler to move around to suit the weather or to facilitate any task at hand. Plus, no one wants to take a coffee break in the greenhouse at the height of summer; inversely, it may be the coziest spot in the garden if the weather turns cold and wet. Furthermore, you should be able to push shelves together to better store your tools and supplies in preparation for winter. Being flexible in your interior design is the best way to maximize your greenhouse’s overall usage and comfort.

Using shelves in the greenhouse is very practical, because it allows you to cultivate vertically and thus have room for many small plants. Even better is shelving that can be dismantled or shelving planks that can be removed, especially since small 50 cm (20”) tomato plants can easily reach 5 to 8 m (16’ to 26’) in height by season’s end, growth that your shelves need to be able to accommodate. Springtime will be the most crowded season in the greenhouse if you pre-cultivate plants, as most of your shelf space will be devoted to many layers of boxes with seedlings. You should not place any boxes directly on the ground (even if there are only a few), because it’s too cold and drafty at floor level; plants do much better when situated a little higher up—which is another good reason to have shelves or a moveable table in the greenhouse, even if you don’t plan on growing that many plants.

The greenhouse will empty out once all the flowers, such as pelargoniums/geraniums, angel’s trumpet and other perennial houseplants, as well as the vegetables, are moved outside. At this point you can remove the shelving to get it out of the way and make room for more living space.

Choose frames and shelves made of metal, as the humidity in the greenhouse will damage wood. On the other hand, wooden shelving is cheap; it works fine when finished and is easily maintained or replaced. Applying some colorful paint adds a nice touch and can match your chairs, cushions or planters. Another bonus with freestanding shelves is that they’re easy to insulate or shade. They have their own framework, so nothing is attached to the greenhouse. By moving these shelves away from the walls, you can also easily insulate the sides of the greenhouse in the fall to prepare for the cold winter months ahead, which is not as easily done with fixed shelving in the way.

There is more outdoor living space in the greenhouse once the plants have moved outside for the summer.

Rimmed trays on freestanding trestles are a convenient setup. They’re easy to water, to separate, and move apart. Ceiling light, used in winter.

Worktables

Tables for cultivating, as well as worktables, can be set up on trestles. A rimmed wooden sheet, like an old-fashioned baking board, can serve as a growing table; the dirt stays contained due to the rim. The top is secured to the trestles with the help of adhesive strips attached underneath to prevent the board from sliding off. As the worktable is moveable, it’s perfect for relocating outside as the weather allows. When used inside the greenhouse, it can stay in the center of the workspace until the planting is done.

Setting seedlings on growing tables makes it easy to care for them. You can choose the work height that suits you; tables can be dismantled and easily moved out of the way when you want to plant bigger plants in the ground, or place bigger containers on the floor. Growing tables made from removable plastic trays set on trestles make watering easier. They come in various sizes, and their low rim makes it simple to water the pots from below, or to use an irrigation mat. It’s also practical in case you want to separate the tables, and have several small trays instead of one large tray.

Separate spaces

In a pinch, garden tables can be used as planting tables, but typically they’re not high enough, not to mention that they quickly become muddy from the spilled dirt. Generally, it’s preferable to keep the workstation and the coffee break areas separate.

There are myriad possibilities in seating arrangements within the greenhouse. Remember that its environment is both humid and warm, so garden furniture meant for outdoor living is what you’ll want to look for—wicker and rattan, for example, or materials that can be easily rinsed off and cleaned. If you want your plants to thrive, you’ll need to be able to wet down the floors and shower the plants on really warm days; by wetting the floors and walls you’re lowering the temperature but are also increasing the level of ambient humidity, and your furniture cannot be so delicate that it cannot withstand this type of atmosphere.

Use what you have on hand. Here’s a simple table, easy to take apart, and it can be used in different ways.

Greenhouse HPS (High Pressure Sodium) light fittings give the plants much needed light.

Lighting

Brightening the greenhouse with artificial light is an option, but not a necessity. If you plan to grow plants year round, or if you’d like to putter in the heated greenhouse over winter, you will need both lighting for the plants and for your workstation. However, if you intend to use the greenhouse mostly for enjoyment and to work in during the warmer seasons, then you won’t need any added light source. Besides, what could be more peaceful and serene than a candle-lit coffee evening in the greenhouse?

Lights will be required in the greenhouse in winter if you want to keep on growing plants, not merely to have them survive. Many plants like geraniums will continue to grow and bloom in the wintertime if they have added light and heat. Others, like the olive tree or the bay leaf, overwinter successfully in natural light and a cool climate, but don’t need extra light.

Moveable solutions

The earliest sowings usually take place between the end of January and the onset of February. By February to early March, newly potted up plants will start to need more space. When there’s no more room on the light-filled window sills but the greenhouse is still too chilly, then extra lighting might be required in the house, but not for very long (see page 33)—four to five weeks at most, after which natural daytime light should be enough. At this point it might even be time to move your plants into the greenhouse.

If you have to cultivate your plants in a space without windows—in the basement or in the garage, say—you can add permanent lighting in that area. As for the short weeks in spring when your plants require extra light, you can deal with this issue pretty simply and temporarily, even if you only use the greenhouse for a short period of time.

Lighting in the greenhouse

Proper light fixtures for permanent greenhouse lighting can be both expensive and heavy. In order to light a large area, the lights have to be set high up, and so must also be of strong enough wattage to shine brightly onto the plants. Commercial growers use HPS (High Pressure Sodium) in special fixtures with reflecting shields. They give off an orange glow reminiscent of Swedish interstate lighting. A light fixture with a light source of 400W is plenty for a greenhouse measuring 10 m² (108 sq ft). A special mini version of the light measuring 70W HPS is enough for 3 to 4 m² (32 to 43 sq ft) greenhouse if it’s placed at about 50 cm (19 3/4 “) above the plants. HPS lights shed more light per watt than their fluorescent counterparts.

Nevertheless, fluorescent lights are easier to find, and remain a very good option for lighting your space; they do however need to be cold white fluorescent lights in order to be used as growth lights. Warm white fluorescent lights are included when you buy the light fixture, and are commonly used to light standard work environments, but they are not good for growing plants. Cold white lights are not expensive; they’re simply not used as often because they don’t give us human beings comfortable lighting in the way warm white lights do. There are also specific fluorescent growth lights available, but they’re more expensive and are not as efficient as the cold white fluorescent lights. Those growth lights are colored tubes containing special spectra for plants, but the plants end up getting less light due to the coating on the tube, so you may as well avoid them.

Metal halogen lights are another good alternative for lighting your greenhouse. They give off a sharp blue-white light; however, they do need to be used with special light fixtures. Plants thrive in this kind of light, and if you’re cultivating in an environment without any natural daylight whatsoever, these are the best lights to use. Cacti and other plants that normally get a large amount of intense light in their natural habitat do best in this type of lighting.

Choice of lighting

Choose lighting according to your needs first. Light fixtures are available at most shopping centers, but the fluorescent tubes typically must be purchased from an electrical store. Permanent lighting should be bought at a greenhouse dealer’s outlet, since the staff understand the structures and their potential problems, and sell fixtures that can handle humid environments. HPS and metal halogen lamps have to fit into special fixtures outfitted with strong reflectors. Typically it’s a fixture that can accommodate either a metal halogen or an HPS lamp. The lamps are pricey, but it’s nice to be able to choose between metal halogen and HPS lights without having to swap out the entire fixture. This type of light fixture is primarily of interest to anyone needing to light an area over a significant stretch of winter, perhaps a space with camellias or citrus trees.

The garden’s coziest room is the greenhouse. Pelargoniums/geraniums, here set on fixed shelving, leave room for a sofa and a table.

Lanterns and candles are enough to make evenings cozy in the greenhouse.

Fluorescent tubes work well above sown trays and boxes. You can choose fixtures according to whether the lights are going to be used in the greenhouse or inside the house, but you must only use fixtures fit for damp spaces within the greenhouse. An effective setup is to mount lights on a shelf unit with adjustable shelves; that way you can move the light up and down as needed. Sown trays placed on top of a shelf where the light tube is attached get heat from underneath and the trays and boxes below get the light—it’s the perfect deal.

All electrical installations must be grounded and connected to a circuit breaker. In up-to-code electrical panels there is usually a common circuit breaker, in addition to a separate circuit dedicated to the greenhouse. Outlets and cords must be approved for use in humid spaces.

Heat from lights

All lamps give off heat, which is why plants stretch towards them. If you’re going to use lights during the winter, it’s a good idea to take advantage of that radiant heat. Lights can be used in the area separated from the rest by insulating plastic bubble wrap. Or make loose plastic tents and hang the lighting inside, but be aware of the fire risk and don’t place the lighting lights too close to the plastic.

Technical installations

Water and electricity are laid out and finished during the greenhouse construction. To be safe, electrical circuits are only to be installed by a qualified electrician. Electricity is needed for lighting and heating; if you enjoy the sound of a water fountain in a mini-pond barrel, remember that this will require electrical work, too.

All outside electrical connections must be grounded and connected to a trip/circuit breaker. You can install low-voltage lighting, pumps and the like (which are connected to a transformer) by yourself without any trouble, as long as they’re made for outside use.