Terrariums are a spectacular way to grow many carnivorous plants. They maintain high humidity, keep temperatures constant, allow in ample light to keep plants happy, and provide a porthole through which you can monitor your plant’s progress. They’re also an elegant way to put plants on display as beautiful indoor and outdoor decorations. Who wouldn’t want to ogle an exotic carnivorous plant through the looking glass?!
Carnivorous plants that do well in terrariums
Venus flytraps (Dionaea muscipula) – Great candidates. They don’t require high humidity, but greatly appreciate it. Flytraps stay relatively small, so are good candidates for ornamental terrariums. Respect dormancy periods.
Tropical Pitcher Plants (Nepenthes) – Will require larger terrariums that maintain high humidity, with some ventilation. Nepenthes are hard to grow outdoors in many areas, so fish tank terrariums and greenhouses are the most common way to grow them.
Sundews (Drosera) – many can be displayed in smaller ornamental terrariums. For larger collections, or plants that need room to spread out (I’m looking at you Drosera binata dichotoma ‘Giant’), larger fish tank-type terrariums will be better.
Butterworts (Pinguicula) – Some species really need the higher humidity of a fish tank terrarium, while others simply enjoy it. Many can be grown in shallow, ornamental terrariums, but remember to respect dormancy periods.
Sun Pitcher Plants (Heliamphora) – Enjoy high humidity, and some get fairly large, so I’d recommend using a fish tank terrarium, here.
Australian Pitcher Plants (Cephalotus) – Enjoy the higher humidity and temperature controls, so use a fish tank terrarium for Cephalotus.
Types of terrariums and when to use them
Enclosed ornamental terrarium – make elegant displays, and bring an old school botany vibe. This makes your already exotic plants look even more curious – like they are specimens imported from a far away land. These terrariums are simple to setup – simply plant the carnivore directly in the terrarium base in the preferred soil mix, or keep your plants in individual pots and place them within the terrarium. You can decorate with ornamental long fibered sphagnum moss. Place them in windowsills for ample light. Be aware of heat that can build up in these containers when they’re exposed to direct sunlight – you don’t want to cook your plants!
Open terrarium – make great centerpieces and give you and your guests the best unobstructed view of your carnivorous plants. It also exposes your plants to the space they are in, which means they can assist in trapping natural house pests. This same exposure does have some disadvantages, though – primarily, temperature will be at ambient room temperature and humidity will be on-par with the room they are in. This isn’t ideal, but many carnivorous plants will adapt. Also keep lighting conditions in mind – you’ll need a sunny windowsill to keep your plants happy.
Fish Tank Terrarium – a more utilitarian option for enthusiastic growers. Fish tanks terrariums require more investment and initial setup, but are much more flexible with the types of carnivorous plants you can grow in them. Use them for larger plants like Nepenthes, or if you have many smaller plants that you’d like to grow. They’re ideal when high-humidity and temperature control is required, such as during seed germination and cutting propagation. They can also be used to quarantine and monitor plants with a pest infestation – to keep them away from other healthy plants during treatment. Tank terrariums are also good for “off season” growing. I’ve always grown my indoor carnivorous plants in fish tanks with florescent grow lights sitting on top. They come in two materials worth considering:
- Glass terrariums – glass is a decent thermal insulator, keeping temperatures inside relatively predictable. Glass tanks will retain heat, though, so cooler grow lights (like LEDs and fluorescents, discussed below) are required. If you’re going to put a glass terrarium outside, it should be out of direct sun – choose a shadier area under a tree or awning. Make sure to also pair your plants with this shadier environment. Glass is also fragile, and will chip and crack relatively easily.
- Acrylic Terrariums – with better light transparency, lighter weight, and greater strength, acrylic terrariums are a great alternative to glass. They are less scratch resistant, so you will have to be careful with grittier soils and sand scraping surfaces.
Fluorescent Grow Lights – florescent terrarium lighting is the best bang for the buck option. Florescents are inexpensive, have a decent lifespan, and are beaten only by LEDs in energy efficiency. Newer generation T5 bulbs will last about 20,000 hours. You have the option of tuning the light your plants receive using bulbs with a cooler or warmer light spectrum. Bulbs in the cooler light spectrum mimic winter months, and warmer bulbs will mimic summer months. It’s good to have both spectrums represented to more closely mimic natural light, but in a 4 bulb setup, you may want 3 of one type and 1 of the other.
LED Grow Lights – the Rolls Royce of grow lights, LEDs are cutting edge lighting technology, cool-running, hyper-efficient, and can last up to ten years. They tend to be more expensive than equivalent fluorescents lights, but like with any newer technology, price is coming down with time. You will save money on electricity bills and replacement bulbs due to their long life and energy efficiency, but the payback period to justify the higher upfront costs may be a few years out. Another neat LED feature is that they often come in light spectrums that are tuned to provide plants with only the wavelengths of light needed to foster healthy growth. This makes them even more efficient than other bulbs that convert energy into wavelengths of light plant’s don’t readily use to build new cellular structures. However, this feature also gives LED grow lights their characteristic pink hue which may be odd mood lighting indoors, and won’t visibly highlight the beautiful colors that many carnivorous plants contain.
High Pressure Sodium Grow Lights (HPS) – a more traditional high-output grow light, high pressure sodium grow lights are good for large-scale growing conditions, but probably not for terrariums. They throw a tremendous amount of lumens, a measurement of the intensity of light, which allows them to penetrate thick canopies of leaves to reach lower branches. They are in the warmer spectrum and give off a yellow-orange light wavelength. Imagine the common orange glow of street lamps at night, and you know what high pressure sodium grow lights will look like. Lifespan is about 20,000 hours, and they are not energy efficient, relative to the lumens/wattage ratio of florescent and LED grow lights. There are also more costs to consider with High pressure sodium bulbs. For instance, most require an external ballast (use a digital one for energy efficiency, to prolong bulb lifespan, and to warm up bulbs faster on startup) to regulate power flow. The bulbs are oval, and suspended horizontally, so you’ll almost certainly want a reflector hood to direct light that would otherwise be directed upwards, to be reflected down towards your plant. There are all-in-one solutions that you should consider if HPS is something you’d like to experiment with. Considering their overall inefficiency at turning watts into lumens, they also produce lots of wasted energy in the form of heat – the bulbs get untouchably hot when they’re warmed up – and this will require venting and cooling in tighter growing areas. If you go with HPS bulbs, be prepared to run the air conditioning frequently, and do not rest the light on top of your terrarium.
Metal Halide Grow Lights – the sister bulb to high pressure sodium bulbs, metal halide grow lights have many of the same advantages and disadvantages as HPS lights. The real difference is that they throw a cooler spectrum of light that mimics natural winter lighting conditions more accurately. Metal halides can be used alongside HPS bulbs for a fuller spectrum, or at different times during the year as replacements to HPS bulbs to produce more natural “seasons” for carnivorous plants. Like high pressure sodium bulbs, metal halide bulbs will produce waste heat, require ballasts, hood reflectors, and are likely overkill for most terrarium setups. Here, again, there are all-in-one solutions, so don’t let me stop you from experimenting!
Monitoring temperature & humidity in a terrarium
Digital Thermometer and Humidity Gauge – Easily readable, digital thermometers and hygrometers are sensitive and accurate, but will require occasional battery replacements.
Analog Thermometer and Humidity Gauge – Analog terrarium hygrometer and thermometers are simple and don’t need batteries, but are a little less accurate and responsive than their digital counterparts. This probably won’t be an issue unless you’re concerned about rapid fluctuations in temperature and humidity.
Controlling temperature & humidity in a terrarium
A small, inexpensive terrarium fan will help with cooling a terrarium, and air circulation in a terrarium. Some air circulation is important for healthy plant growth and helps reduce mold and fungus problems. Place the fan at a top opening of your carnivorous plant terrarium, and angle the airflow down, into the terrarium. Try to avoid creating a windstorm for your plants by angling the fan against a pane of glass. It’s a good idea to put a fan on a cycle timer to have it turn on every fifteen minutes for one minute. This keeps fresh air and circulation good, and avoids vacating too much of the valuable humidity.
Under Tank Heating Mat and Heating Controller – Heat radiated by florescent grow lights will go far in warming your terrarium. In fact, I frequently have to put spacers between my florescent lights and the top glass of my terrarium to create an air gaps and keep the tank cooler. If you rest the light fixture on top of the tank, you’re not likely to have issues keeping the tank warm, but there are exceptions. If your terrarium will be in a cold corner, use a heating pad or seed germination mat under the base of a fish tank style terrarium to increase temperature by a few degrees. Pair it with a controller that will automatically, actively monitor temperature, and turn the heating element on and off to maintain a steady environment.
Feeding carnivorous plants in terrariums
Live Mealworms – These little critters can easily be purchased online or picked up at pet food stores, and are great for Nepenthes, Cephalotus, Heliamphora, and large Venus flytraps. Drop these directly into the plant’s trap. Keep them refrigerated between feedings to prolong their lives and viability as plant food.
Live Crickets – Good in tanks that don’t have water pooling at the bottom (otherwise they’ll drown and rot). Similar to meal worms, the are good for Nepenthes, Cephalotus, Heliamphora, and large Venus flytraps. Keep in mind that crickets do “chirp,” so don’t use live ones if the noise will bother you.
Wingless Fruit Flies – these come as kits that you can use to grow your own fruit flies, which make great food for Sundews, Butterworts, small Venus Flytraps, and even Nepenthes. Once grown, simply puncture a small hole in the top of the lid, turn the container over, and sprinkle your plants with food. Reseal the lid with tape to prevent fruit fly escape.
Dried Insects – for folks not into the idea of feeding live insects to their carnivorous plants, here’s a simple solution: dead insects! This option is a bit of a grab-bad of different critters that can be fed to plants for a well-rounded nutritional mix. Pick up a pair of forceps, and you won’t even have to touch them!
I hope this clearly outlines all of your options and helps you decide which carnivorous plant terrarium setup is right for you. With all of these considerations, it may seem a little daunting, but follow the recommended links and you’ll be off to a good start. Leave comments and questions below and I’ll be happy to get back to you with answers! Cheers, and happy growing!