Making an Indoor Terrarium ©2000 R.Sacilotto

Terrariums are a fun and fascinating way to grow many indoor, tropical, carnivorous plants that like the high humidity that terrariums provide. Temperate species that require a cold winter or plants that need full sun are generally not good terrarium subjects. Monkey Cups, (Nepenthes), Sundews, (Drosera), Marsh Pitchers, (Heliamphora), and the Australian Pitcher Plant, (Cephalotus), are all good choices as long as one pays attention to the needs of each plant. Select cool, 55-75° F, or warm,65-85+° F, growing plants, depending on your conditions. Natural diffused/shaded sun or fluorescent lighting can be used. The diagrams below illustrate some of the basics of successful terrarium design. In addition to plants and the ingredients described below, you will need some sort of clear cover that can be opened more or less to provide ventilation. Two pieces of glass that can slide together or apart are what we use. Shatterproof plastics may be wiser if young children are apt to handle the tank cover. Use fairly thin material for best light transmittance. Glass shops will usually cut and polish/grind sharp edges off if you give them measurements. Don't forget lighting and an inexpensive siphon to drain excess water. Maintenance tips follow construction.

Terrariums are heavy and are best built where they are to stay.

Side view

Step 1: Add 1 1/2 inches of slightly damp,coarse sand to cover the tank bottom.

Step 2: Arrange non-alkali stones, (no limestone or marble), to form a well, pool facing the viewing side. The well may be in the middle or off to the side, but center placement makes siphoning easier later on. Be careful not to damage the tank with the stones. As you proceed, use soil mix to position stones.

Step 3: Add soil mix first around stones for support, then raise to the desired level. Be sure that the stones do not lean toward the glass! They should slant away from it so they won't easily tumble onto it. Sphagnum moss can be used to plug large cracks in the stones so the soil mix won't leak excessively into the well. Soil mixes include: 40%sand + 60%peat moss for small sundews, 30%perlite + 70%Sphagnum for Heliamphora, Cephalotus, many large sundews and most Nepenthes. Nepenthes also may prefer 30% orchid, (fir), bark + 40%sphagnum + 30% perlite. Consult plant care guidelines for individual plant needs regarding soil type.

Step 4: Press live or dried Sphagnum moss into surface. Other surface coverings may be used such as bark, stones, pine needles, etc. Small sundews are best planted on bare peat/sand mix with no live moss around them as moss can quickly bury small sundews. Sphagnum or peat can also be used to hide perlite, next to the glass or on the surface, if this is desired.

Step 5: Move the moss or surface covering aside where the plants are to go and set the plants in place. Plants can be planted in pots to provide localized soil type or planted directly into media. If planted in pots, be sure pots have drainage and don't forget to water these plants within the pot. Often, roots will grow out of pots into surrounding media. After planting, any surface covering can be repositioned. Keep live Sphagnum away from plant stems. Water in your plants.

Step 6: Cover the tank with a clear material that can be adjusted to provide ventilation. Usually, about 10% of the top should be kept open. The vent is best located in the middle or along the facing side as this helps keep the glass from fogging up so you can see in the terrarium. If all sides are usually covered with condensation, then the vent size should be increased until only a little or no water stays on the sides. Next, add lighting. Do not supply full sun or the terrarium will overheat. Dappled sun or sun filtered through sheer fabric or house plants can work. We use 4 fluorescent bulbs per 10-12 inches of tank width, suspended barely over the tank cover. 50% wide spectrum plant light,e.g.Gro-lux™, and 50% cool white, installed by alternating each type, is our favorite lighting. Spot lights can be too hot. See the following maintenance tips, for more important information.

Water: Use fairly pure water such as distilled, rain or water that has been put through reverse osmosis filtration. Most kitchen-style cartridge filters do not remove salts that can be harmful to plants. Since purified water usually has had much of the oxygen removed, we strongly recommend aerating the water by half-filling a clean, covered jug and shaking it thoroughly to mix air into the water. Rain is naturally aerated and doesn't need this step.

Since terrariums are very humid, water splashed on the leaves and in the crowns of plants will not dry quickly and encourage disease. Water around the plants and try not to wet the leaves excessively.

Usually, a good soaking once a week or so is plenty; water around the plants thoroughly until water collects in the well that was made during construction. After a few minutes, siphon the water out of the well into a jug or bucket. This washes the soil of mineral salts as well as gives the plants moisture. If you only add a little water each time, salts can enter the terrarium but can't leave if you don't siphon water out. While this may not be a problem for awhile, minerals eventually concentrate in terrariums that don't get siphoned. In our experience, this salt build up is the biggest reason terrariums look great for awhile and then decline. Pet stores carry cheap siphons and often a new siphon made for kerosene use will work, as long as it's never used for fuel! Positioning the siphon suction end can be tricky so taping or tying it to a slender stick, that can reach the well, makes the job easier. You might suck up a little sand or soil, but that should decrease in time. A little water left in the bottom is not a problem, but don't leave the terrarium deeply flooded for long periods. The greater the purity of the water used, the less siphoning and leaching is needed. Normally, a good flood/siphon is done once a month.

Feeding: Feeding: Avoid fertilizing carnivorous plants. A few small insects, dead or alive, placed in or on the traps, will provide enough nutrients for most insectivorous plants. Once a month feeding is plenty and most carnivorous plants can go for months without insects. Many Pitcher Plants benefit from a weak solution (1/4 strength) of Miracid fertilizer placed only in the bottom half of the pitchers. Fertilizing the root zone is not recommended. If the plants look healthy, avoid fertilizer altogether.

Lighting: It's important that the plants receive bright, indirect or dappled light. While direct sun will usually cook or sunburn the plants, too much shade will cause stringy growth and poor coloration. Different plants have different needs, but a good starting place is to use four fluorescent tubes for a tank that is 12-14 inches wide. The length of the tubes should be as long or longer than the tank.

We use 50% Gro-Lux® plant lights and 50% cool white, placed alternating across the top. The lights should be barely above the tank cover and the plants from 4-7 inches below the lights.

Spot lights put out more heat and less light and are not recommended. Natural sunlight can be used if it is filtered through a sheer fabric, white plastic or partially shaded by other plants that do not have large, broad leaves, (too dark). Watch your plants and adjust the light as needed. Spindly, thin and stretched growth indicates not enough light whereas pale yellow leaves with burned edges indicates too much light. For those of you with light meters: place the sensor in the tank and under the cover. When the sun or lights are illuminating the terrarium, an average candlepower runs from 500-800 using natural light, and from 400-600 using the above fluorescent lights. High Pressure Sodium and Metal Halide are usually at 600-850 foot candles. These general guidelines may need to be adjusted according to what you are growing. In any case, do not let the lighting run the terrarium temperature above 95°F.

Maintenance: Look at your plants to see when they need pruning or the removal of dead leaves. Sometimes, moss will grow vigorously and require pulling or trimming away from plant stems. Some sundews, such as Drosera adelae, can grow from runners or roots and need to be thinned out. Plants growing too close to the cover, such as Nepenthes, often need horizontal training or pruning. Some plants may even get so large as to require removal from the terrarium. This is especially true of larger growing Nepenthes which were planted in the terrarium as seedlings or small tissue cultured plants.

Keep the cover clean and free from excessive dust as dirt can dramatically decrease the light the plants get. If using fluorescent lights, replace the bulbs after they dim, the ends darken or light output decreases.

Use a damp cloth or paper towel to wipe the inner glass when it gets dirty. Do not spray window cleaner into the tank! If you must use it to remove interior grease spots or dirt, then put a little on the cleaning cloth or paper. You can spray cleaner on the outside surface of a glass tank, as long as the cleaner does not contact the plants inside.

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