In principle it's possible to keep carnivorous plants in a closed terrarium. Some species work a lot better than others though. Additionally, those better suited need certain accommodations to feel at home. Especially the substrate plays an important role for the survival of carnivorous plants in closed terrariums.
Important! In this article I'm speaking specifically about carnivorous plants in closed terrariums. If you want to know all about building a closed terrarium in general, I recommend you read the ultimate guide.
Why are some plants carnivorous?
Most people know venus flytraps from their local gardening center or hardware store. But they're by far not the only type of carnivorous plants. Currently scientists believe that carnivory developed independently at least 9 times. This happened in 5 orders of plants and thus, seems to be a good way of getting nutrients in not so nutricious environments. That's the keyword here.
Tip: It can be hard finding supplementary plants that also require few nutrients. Thankfully, moss saves the day!
Nutrients are the keyword here
Carnivorous plants live in soils devoid of nutrients and thus, have to look elsewhere to get them. Soils harbouring carnivorous plants are mostly missing nitrogen. Most of these plants can be found in swamplands like the venus flytrap. This gives us a hint how to mix our substrate.
If you want to learn more about insects and other animals in closed terrariums, read this article.
Different kinds of trapping mechanisms
First I want to show you the different kinds of trapping mechanisms. Then I'll show you which of these are suitable for a closed terrarium. There are many species using the following trapping mechanisms:
- Snap traps (like the venus flytrap)
- Flypaper traps (like the sundew)
- Pitcher plants (Sarracenia)
- Lobster-pot traps (also Sarracenia)
- Bladder traps (Ultricularia)
All carnivorous plants utilise one or more or these trapping mechanisms. Lobster-pot traps for example use hairs hindering the insects to turn around and walk back out. Some pitcher plants use this technique as well. Let's start with snap traps.
Snap traps, like the venus flytrap
Since venus flytraps (Dionaea muscipula) are the most well-known carnivorous plant, they are also the most-well known snap trap. They originate in the Pocosin wetlands in the US. Nowadays they're a beloved houseplant. You can buy them in pretty much any gardening center or hardware store.
How they work
Young venus flytraps start out with one large root that dies off very quickly and leaves smaller hair-like roots behind. These roots are only used for absorbing water and cannot really absorb any nutrients. Instead venus flytraps depend on their bear-trap like blossoms to get nutrients. Inside each of those are small sensory hairs needing to be touched to activate the trap. It's important that at least two of those get activate in a timeframe of 30 seconds. That's to prevent the plants accidentally closing due to dirt or rainfail.
How you usually keep them
Usually venus flytraps can the kept effortlessly in a pot at home since there are more than enough small insects flying around. In a closed terrarium that can be a little different. The fewer nutrients are in your substrate, the more your venus flytraps depend on insects. Sadly, your closed terrarium cannot keep up with that demand. If your substrate is rich in nutrients your plant will slowly stop developing new traps which doesn't look really nice either. Alternatively you can always open up your closed terrarium to let in some bugs. But that's not really the idea here, is it? So how can you best keep them in a closed terrarium?
How to keep venus flytraps in a closed terrarium
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Since venus flytraps originate in swamplands, you should try and replicate that kind of substrate in your closed terrarium. It should especially be able to let water run through it freely. You can use your usual kind of substrate here that's not susceptile to compaction (e.g. by adding dried sphagnum moss or coconut fibre). To create an authentic swamp substrate you can add a little bit more moss or coco fibre than usual. Sand and perlite are also good additions. What's also very important for a good flow of water is a false bottom. You can learn how to make one in this article.
How much water, how much sunlight?
After planting your venus flytraps you should water them so the entire subtrate is wet. Usually you'd wait with watering for the subtrate to become dry again but that's not really possible with the daily water cycle. There'll always be water in the ground. Of course your plants need sunlight as well. Bright indirect light works best. They can also tolerate direct light but shouldn't get more than 4 to 5 hours daily.
The temperature is not that important
Most time of the year you won't have to worry that much about the temperature. Your room temperature of 20°C is very suitable for venus flytraps. Starting in November, they'll prepare for the winter though. During winter, a temperature of 0°C to 10°C is best for them. They should be kept at this temperature until about February. Durint winter, their traps become inactive and start shrinking a little bit. If it's not too cold you can keep them outside. However, if the temperature drops below -5°C you should take them back inside and maybe put them into your fridge. The 7°C to 8°C in there are optimal. Much more information about venus flytraps is available at Plantura Garden (it's in German though).
Keep note that venus flytraps reach their final size after about 3 to 4 years. If you're careful with them, they can even live up to well over 20 years!
Flypaper traps, like sundew
Another beloved kind of carnivorous plant is the sundew (Drosera tokaiensis for example). It belongs to the flypaper traps and is known for its long, sticky tentacles (yeah, they're also called tentacles for plants). It's important to mention that sundews are a genus and not a single species. There are over 200 species, all of which need about the same conditions. So we can easily sum up how to keep them all.
There are five different forms of sundew.
- Temperate sundews (mostly in Europe)
- Subtropical sundews
- Pygmy sundews
- Tuberous sundews
- Petiolaris complex
Sundew depends on insects
The subtropical form of sundew is most interesting for closed terrariums since it looks about the same all year round. The temperate form is protected by natural conservation in Germany (where I live) and might be in your country as well. If you ever find one, please don't take it with you. Just like the venus flytraps, sundews have very inferior roots. Most times these are long taproots reaching very far into the ground compared to the height of the plant up above. These roots are really only used for absorbing water and don't take in many nutrients. Most kinds of sundew even lack the enzyme nitrate reductase used for utilising nitrogen from the ground. Instead, they're completely dependant on getting it from insects.
Bad news for sundews
The lack of this enzyme is bad news for keeping sundews in closed terrariums since they need a constant stream of new insects. Introducing a large colony of insects into a closed terrarium with sundew will lead two most of them sticking to it in a very short time. This problem doesn't really arise with venus fly traps since the traps actively close. Sundew however, is always sticky and will catch easy and every insects it comes into contact with.
So sundew isn't really suited for a closed terrarium. You can of course open it from time to time to let insects fly in. You can also throw in some dead insects. But that's not really a closed terrarium. If you want to go this route anyway, I'll now tell you how to keep sundew.
How you can keep sundew anyway
A beloved member of the sundews is Drosera capensis or Cape sundew. It originates from South American swamps and thus, needs similar conditions in your closed terrarium. It's generally seen as easy to maintain and really likes wet soil. That's quite helpful for your terrarium since you don't need to be quite as delicate with your watering. However, it's really important that you use lime-free water. Distilled or rain water works well here. Your room temperature is also perfect for Cape sundew. It's not harmful if it gets a littler warmer. If you have any more questions, there are answers on Gartenjournal (also in German, I'm working on English sources).
Pitcher plants, like Sarracenia
As the last member of carnivorous plants I want to introduce you to pitcher plants. They are most memorable for their long tube-like leaves with a very slippery surface inside. They are beautiful to look at due to their red-green color gradient and fit many backgrounds. Wouldn't it be great to keep them in a closed terrarium?
First let's look at the trapping mechanism. Almost all species of this genus have four discrete zones in the tubes.
- First zone: Operculum
- Second zone: Trap entrance
- Third zone: Middle of tube
- Fourth zone: Bottom of tube
What are all these zones for?
The operculum is used for keeping rain out of the trap so it doesn't fill up and tip over. That's not really necessary in a closed terrarium but it's not harmful either.
The trap entrance is right beneath the operculum and features many hairs. The front part features the so calls peristome that's responsible for producing nectar to attract insects. The insects get a false sense of security due to the many hairs which they can easily hold onto. They crawl further and further into the tube.
As soon as they reach the middle part of the tube, it's already too late. This part doesn't have any hairs and is very, very slippery. Before even realizing it, the insects are falling to their doom and find themselves in the lower part of the tube.
This part is filled with digestive fluid to digest the insects. Additionally, there are downward facing hairs again to keep the insects from crawling back up.
Good news for your closed terrarium!
Pitcher plants do have, in contrast to sundews, the enzyme nitrate reductase and thus don't rely on insects to survive. They just need fitting soil and enough sunlight everyday. Just like venus flytraps and sundew they originate from swamplands with soil devoid of nutrients. You should replicate those conditions. You can use peat mixed with sand for your substrate. Just don't use sand from the sea. This has a lot of lime and salt which is harmful for your pitcher plants. If you don't have peat, you can again use soil from your garden and mix it with dried sphagnum moss and coconut fibre to ensure a loose substrate resisiting compaction. You can read more about substrates here.
How to keep sarracenia in a closed terrarium
Just like for the other carnivorous plants, room temperature is very fitting. It can be a little warmer without harming your plants. The soil can be quite wet as long as there is no standing water. This is best done with a false bottom. Just like venus flytraps, pitcher plants need different conditions during the winter. You should keep them at 5°C to 10°C. You can either do that in your garden or your fridge if there's room left. There really shouldn't be anything keeping you from having pitchers plants in a closed terrarium.
Now you know quite a bit about venus flytraps, sundew and pitcher plants and whether or not you can keep them in a closed terrarium. If you ever notice something going bad in your closed ecosystem you can of course always open in up. All the plants I showed you produce sweet nectar so it shouldn't take long to attract some insects.
If you want to find out even more about suitable plants for closed terrariums, read this article here.
Summary
Venus flytraps and pitcher plants can be kept almost effortlessly in closed terrariums as long as your substrate is devoid of nutrients and water can flow freely. Sundew runs into the problem of lacking the enzyme to take in nitrogen from the ground. You should regular open up your closed terrarium when keeping sundew so insects can fly in.
Do you already have a closed terrarium with carnivorous plants?
If you've already built a closed terrarium with carnivorous plants, be sure to send me a photo to jan@terrarium.blog or on Instagram @terrarium.blog. I myself don't have one yet and would be very curious to see yours! I'll gladly link your profile name and share the photos with the world.
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