Terrific terrariums

By strict definition, a terrarium is a tightly closed clear glass or plastic container filled with small, growing plants. Through common usage, the term has come to also include an open transparent container used for growing and displaying plants.

Terrariums were discovered by Dr. N. B. Ward of London. He was studying the emergence of a sphinx moth from the chrysalis buried in moist earth kept under a glass. He was amazed to see a seedling fern sprout and grow under the glass. That fern grew for four years under the glass without anyone adding one drop of water to the soil, nor during those four years was the glass cover ever removed from above the fern.

Almost any clear plastic or glass container, such as an aquarium or canning jar, can be used as a terrarium, or you can purchase a terrarium or "conservatory" specifically designed for that use at a local garden center. Make sure the container has sides and a top made of clear plastic or glass. Any tinting of the plastic or glass will drastically reduce the amount of light transmitted.

Initially wash the plastic or glass to eliminate any streaks of dust or dirt. Use a dish-washing detergent and thoroughly rinse and dry. This process sterilizes the glass so that no disease spores are present inside the terrarium. If you use a glass cleaner that has ammonia in it, air out the terrarium for several days before planting.

Next place a combination of soil and drainage materials in the bottom of the terrarium. About one-fourth to one-fifth of the container volume should be used for these materials. First place a layer of 1 inch to 2 inches of small gravel for drainage on the bottom of the terrarium.

Now cover the gravel with a half-inch-thick layer of horticultural charcoal. Charcoal absorbs gases and chemicals that may become noxious to plants.

Place a thin layer of sphagnum peat moss above the charcoal. This layer acts as a barrier to separate soil placed above from the drainage material below.

Finally place a layer of moist, sterile potting mix above the sphagnum peat moss. Do not use a heavy potting soil or garden soil. Both products may harbor disease organisms and will stay too wet. The depth of the soil may vary depending upon what type of scene that you may want to portray in the terrarium.

Next plant the small plants that you have selected for your terrarium. You may want to have one unusual and showy plant as the focal point, and surround it with other small plants. Use plants that grow rather slowly and have a low, dense growth habit. You may want to even use moss as ground cover over the soil between plants. Be sure to select plants that have similar light and moisture requirements. For example, you don't want to place a cactus in the same terrarium as a ficus.

Do not fertilize your plants. You want them to grow slowly. Over fertilization will cause excessive plant growth and result in the need to constantly prune the plants in the terrarium to keep them in check.

If your terrarium is a closed container, cover it with the lid and place the terrarium in an area that gets medium to high indirect light. Never place a terrarium in an area where direct sunlight will shine on it. Direct sunlight will cause the temperature inside the terrarium to raise drastically, maybe even to the point that plants will be killed.

Once your terrarium is completed, do not water it until you see plants wilting from drought, or when you observe that moisture no longer condensates on the side of the container. In a closed terrarium, watering may only need be to done every few months. When you do water, water very lightly. If you water too much, your plants will be swimming in water and eventually drown.

If your terrarium is an open container, you will have to water a little bit more often. Let your plants indicate when they need water. When they are dry, they will begin to wilt during the day, and become turgid at night. When you do water, water lightly so you don't drown your plants.

If you like to garden, but don't have the space outdoors a terrarium is a natural choice. You can grow plants inside your home or apartment, with a minimum of effort and space, and still enjoy a touch of nature.

Send your gardening and landscape questions to Paul Schnare at P.O. Box 699, Cape Girardeau, Mo. 63702-0699 or by e-mail to news@semissourian.com.