Cultivating Carnivorous Plants (2015)
GROWING CARNIVORES INSIDE
A terrarium in the author’s living room.
Most carnivorous plants growers keep at least one carnivorous species inside. Like the outdoors, the
indoors also has many different environments, some of which are more suitable for growing carnivores and
others that are less suitable. Indoor growers need to assess their indoor areas for not only the plant’s basic
needs of water and light but also for humidity and temperature.
The most basic indoor set-up is a sunny windowsill. Many carnivores will do well on a windowsill. The
easiest way to care for them is to place them in a small plastic tray and to fill that with water, never allowing
the water to dry completely. This method of watering is called the “tray method.” East-facing windows are
good for plants that prefer cooler temperatures, while west-facing windows may allow for longer exposure to
the sun, depending on the location of the grower’s house. In the northern hemisphere, south-facing windows
CULTIVATING CARNIVOROUS PLANTS
will have the most ambient light. In the
windows will have the most ambient light.
For more specialized carnivores, growers
often turn to terrariums. These can be
constructed of glass or plastic. For long-term
use, glass is preferable. For easier or younger,
plants, a terrarium on a windowsill works well.
Note, however, that a terrarium in direct sun
can heat up tremendously, causing a plant to
die due to heat stress. Therefore, any
terrarium should be accompanied by an in-
terrarium thermometer or tested with an out-
of-terrarium thermometer on a regular basis to
ensure that it is not becoming too hot for the
Once windowsill space runs out, growers
often turn to grow lights. These come in
several varieties, but most growers use either
florescent lights or LED lights. (It is also
possible to use metal halide, high pressure
sodium, or incandescent lights). The reason
for the widespread use of florescent lights and
LED lights is twofold: 1.) these types of lights
are cheaper to operate than other types, and
2.) these lights are widely available thanks to
recent advances in lightbulb manufacturing.
After running out of windowsill space,
An indoor setup using T5 lights (top) and LED lights
growers often have to find “grow racks.” Most
(bottom). LEDs often come in blue and red, rather than
growers use whatever shelving that they can
white, as is common with T5 lights. This is due to those
find. Oftentimes, these shelves are wire racks.
colors closer match to the photosynthetic wavelengths
These racks work extremely well for hanging
needed for plant growth.
light fixtures and running wires, but may be
prone to rusting.
In order to provide a stable base, most growers acquire a number of nursery trays, which they will place
atop the shelves and fill with water. Nursery trays are often made of thin plastic that becomes brittle over
time. I recommend investing in heavier plastic trays, made of rubberized plastic. These will outlast the
cheaper nursery trays by years, and, ultimately save money as they will not have to be replaced as often (or
suddenly spring leaks!).
Artificial Light Considerations
Until recently, most growers used any florescent lights that they could their hands on. Nowadays, most
use T5 lights, often in two-bulb or four-bulb arrays. There are innumerable companies that advertise their
bulbs and arrays as “grow lights” but, in reality, the key to good plant growth is the wavelengths of light and
its light intensity. The most valuable comparative measurement of lights is the Photosynthetic Active
A typical indoor setup using an open terrarium, reflective Mylar, and 4-bulb, T5 light unit.
tion (PAR) value, i.e. the actual amount of energy being used by the plant for growth. This is not often
available on the packages of lightbulbs. In terms of actual information available on lightbulb packages,
including LEDS, the wavelength of the light produced by the lightbulbs is sometimes available. Chlorophyll
absorption peaks at 430 nanometers, 453 nanometers, 642 nanometers, and 662 nanometers.
When setting up a terrarium with lights, it is important to have a thermometer inside the terrarium.
Oftentimes, lights will be placed directly above the terrarium, which causes a lot of the heat produced by the
light array to enter the terrarium and heat it. In order to avoid some heat buildup and stagnant air, it is
advisable to have a small, computer-type fan inside the terrarium or to keep a lid a bit ajar.
Most species will prefer artificial light set on 8, 10, 12, or 14 hour cycles. Of course, the exact amount of
time artificial lights should be on depends on the strength of the lights. As a general rule, light loving species,
such as most Nepenthes, should exhibit beautiful colors under the lights. If colorful species are near maturity
and still, largely, green, light needs to be increased.
In addition to lightbulbs themselves, light may also be increased through the addition of reflective
coatings on the backs of terrariums or behind plants. The cheapest way to do this is to acquire “emergency
blankets” made of Mylar and cut those to fit behind the plants. While this will not significantly increase light
available to the plants, it will increase it enough to result in slightly better coloration.
CULTIVATING CARNIVOROUS PLANTS
Terrariums are an easy way to increase ambient
humidity. Completely closed terrariums can increase
humidity to near 100%. Open terrariums can increase
terrariums 20% - 30% more than the outside air. How
much humidity needs to be increased dictates whether a
terrarium should be opened, partially closed, or
Many growers adapt aquariums into terrariums. The
advantages of aquariums are many. They are cheap. New
tanks can often be found for $1 a gallon, and used tanks
sell for even less. Glass shops, which can custom cut
tops, abound. These shops often charge around $20 for
a simple glass top for a 20 or 29 gallon tank, the size of
many collectors’ terrariums. Egg-crate for florescent
lights or live sphagnum can be placed on the bottom of
the terrarium to keep the plants from sitting in water.
Grow light fixtures are often sized to fit, almost exactly,
over the tops of aquariums.
drawbacks. Tanks larger than 55-gallons often become
very expensive, and are priced much higher than their
component parts. Further, even 55-gallon tanks are
cramped for many species, once they get close to
maturity, as the tanks are often long and narrow, rather
than wider and taller. As a consequence, growers with
larger collections often turn to grow-tents, greenhouses,
or custom-built terrariums. All of these require some
level of technical expertise beyond the simple terrarium.
When possible, it is advisable to grow plants
outside of a high-humidity environment. For some A grow rack with both plants growing in the open
species, this is impossible, but, for many species, they
air (lighted) and plants growing in terrariums
can adjust to a lower-humidity environment. The
(dark). This mixed-use of grow racks is common
advantage of avoiding a terrarium is not just cost.
in larger collections which contain plants with
Avoiding a terrarium also prevents terrarium-specific
different humidity needs.
problems, such as stagnant air breeding fungus, from
occurring and harming one’s collection.