I continue to receive more and more requests about growing orchids inside a terrarium. I am suspecting that there are many more people making the transition from growing on the windowsill to a more enclosed space where they can control conditions like humidity much better. One of the advantages of setting up a terrarium is the fact that you can create a self-contained miniature environment quite easily. However there are several factors to keep in mind when doing so, hence I have put together this web page in an effort to address these issues for the orchid grower. If you have a question that is not addressed here, please let me know and I will do my best to incorporate the answer here for everyone's benefit.
If you are using an old aquarium, there is fairly little to do. Provided it was a fresh-water tank, then you will need to just clean it thoroughly with a mild dish-washing soap, and rinse thoroughly. If it was a salt-water tank then you will need to repeat this several times, and possibly let it sit full of plain water for a couple of days in between cleanings. The reason for this is that any residual salt will definitely cause you grief down the road. Hence it is best to deal with this right up front.
Choose a location where direct sun will never hit the tank. The glass of the aquarium will amplify the effect of the sun's rays resulting in more of an oven, than a terrarium. Leave at least 1 inch between the tank and any window surface to buffer the temperature changes happening outside.
If you only have a location with minimal direct sunlight, you might consider adding some white reflective background to offset the amount of light hitting the tank. It may be wise to place a min/max thermometer inside the empty tank for a couple of days once you have placed the tank in it's intended location. This will avert any nasty surprises down the road, and avoid needing to relocate after the tank is set up.
I would avoid using soil, sand or gravel as a substrate for your tank. It is difficult to do any maintenance once these materials are in place, and they can easily sour the environment. I would sooner use a layer of egg-shell crate to serve as the base to build on. This will provide air below the pots, and keep the plants above any water that accumulates on the bottom. Then if you ever need to do some house-cleaning, it is easily removed and the tank can be scrubbed before setting it up again.
Egg-shell crate is the material used as fluorescent fixture covering. It has spaces about 1/4 inch square, and it is about 1/2" high. It can easily be cut to size with a jig saw, utility knife or pruning shears.
If you want to create a realistic snap-shot of the forest floor, you will probably want to introduce a few props for things to grow on, or serve as a background for choice plants. Remember that everything that goes into the tank should be scrutinized carefully, and cleaned properly before entering.
Some good choices for props would be driftwood, such as can be purchased from an aquarium store. Other interesting surfaces can be virgin cork (because of it's rough surface. Even a couple of these placed up against the back can look like the base of a tree trunk growing into the forest floor. Rocks can also be used quite effectively. If you collect your props from the outdoors, be sure to clean them properly. You can use boiling water with some bleach added to sterilize the props, and then rinse them thoroughly. Don't do this in an enclosed space, as the bleach fumes will be overwhelming !
It is always more effective if you use a least a few companion plants that are not orchids to make the environment more varied and interesting to the eye. Choose plants that remain very short, or are very slow growing. All plant candidates must be able to tolerate high humidity at all times to make suitable candidates. Some good choices are low ferns, ivy, peperomia, short nephthytis, fibrous-rooted begonias, rhoeo, selaginella, short crotons, small dracaenas. You can find many of these that are variegated or spotted with white, pink or red. These choices can provide some color when your plants are not in bloom, but keep them to a minimum, otherwise the setup can look too busy and less natural.
Besides the filler plants, you can also use companion plants that normally occur with orchids like members of the bromeliad family. Tillandsias and cryptanthus are great choices and will also bloom, producing very exotic flowers. They can even be attached higher up on the props to really give that realistic jungle appearance. Bits of spanish moss can add that Louisiana Bayou effect if you drape them from the top of the props. Spanish moss also produces very fragrant tiny flowers as an added bonus.
You need to choose your orchid candidates carefully. For the most part they should be plants that like lower light/intermediate temperature/high humidity. Depending on the size of your terrarium, it makes sense to choose plant sizes that are in scale with the dimensions as well, as it will look more pleasing. Fortunately there are many great candidates to choose from.
Miniature candidates are masdevallia, pleurothallis, promenaea, dracula, ornithocephalus, aerangis, angraecum, bulbophyllum, barbosella, leptotes, sophronitis, dendrobium, psygmorchis, etcetera, along with anything identified as a "twig epiphyte" in books.
You will also find compact candidates from the genera mentioned above, along with paph species, cochleanthes, phal species, jewel orchids, etcetera. Unless the mature size is clear in a description, it is always best to ask your plant source whether or not the plant is suitable for a small/medium/large terrarium.
Place the egg-shell crate on the bottom. Put your props in place. Now place your larger filler plants towards the back and shorter towards the front. Now place your orchids, ideally so that they are not crowded by the filler plants. You can fill any empty spaces with a little sphagnum moss, as it will usually begin to grow under ideal conditions. I would use it in front of plastic pots to help hide them.
Initially, the terrarium may look a little dishevelled, but don't let this depress you. Allow the plants a little time to adjust and start to grow, and usually within a couple of months things will start to look terrific.
It is best to use only rain water or distilled water for your plants, as there is no way to leach out accumulated salts from the pots. Misting lightly with plain water every 4 days or so should be sufficient. This will be determined by the location and venting. Humid air tends to sink, so little of the moisture will escape unless you have fans going.
I would NEVER fertilize more than once a month, and even then only at a very reduced concentration to avoid salt build-up. One eighth of the recommended strength on the label is probably suitable.
You can use a standard aquarium hood fitted with fluorescent tubes to provide supplemental light if your location exposure is too dark. I would avoid incandescent tubes as they give off too much heat. If you have no choice, then ample venting may be sufficient to dissipate the additional heat.
In smaller tanks, this is most likely not an issue, but larger tanks may require supplemental air movement. This can be provided through small fans purchased at an electonic or computer store, and attached to the back of the tank hood to provide gentle air movement inside the tank.
When it comes time to repot, it will be easier as the plants have remained in their primary container. Just pull out the plant and replace the media, and then put in back in place. Don't drench the new media before replacing the plant as a little dryness will help to heal any root damage that occurred during repotting. If your plant is a rambler like many of the bulbophyllums, then you can ignore the need to repot, as it will have attached itself to other surfaces in the terrarium, and will be quite content to be left alone.
As more information is needed, this page will be updated.
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