Try Something New - Terrariums
Rebecca Magron, Horticultural Consultant & Research Associate
Dated -
December 27, 2007

The holiday season rush may begin slowing down for many of us, leaving ambitious gardeners with some time on our side to try something new. Terrariums can be a challenge as they are not easy to establish and maintain, but there is something very intriguing about a miniature landscape under glass. Added bonus: it’s a great activity for older kids while they are home from school and a good excuse to use an old fish tank that has been taking up precious storage space.

Three of the most common terrarium themes are bog, desert and woodland, but there are many more. A few basic things are needed to get started: a container, gravel, soil and, of course, plants. As mentioned, an old aquarium makes a fine container, but most clear glass or plastic containers, such as a mason jar, will suffice. Preferably, the container should have a clear lid.

After you have your container, the next critical step is to decide on what plants you are going to use. In general, plants should be slow growing and have similar growing requirements to each other. If you choose a theme, then the plants you choose should naturally occur under similar conditions in the wild. Some plants that are good candidates for a bog themed terrarium include carnivorous plants such as Venus fly trap, pitcher plant, and sundew. Prickly pear, aloes and other cacti or succulents are appropriate for a desert garden. Finally, club moss, ferns and seedling pines are popular in woodland terrariums.

Add at least one inch of gravel mixed with pieces of activated charcoal to the bottom of the container. The gravel will provide drainage, while the activated charcoal helps to purify against some bacteria and keep odors at bay. Then add one to two inches of soil. Use potting soil appropriate for the types of plants you intend to grow and add sterile sand. The planting medium in a bog should consist of either live sphagnum or peat moss mixed with some sand. If using live sphagnum, soak the moss at least 30 minutes in water and squeeze out excess water then place a layer 2 to 6 inches thick. For a desert terrarium a 2:1 mixture of sand to potting soil with some peat moss should be sufficient. A woodland terrarium should do well with a 2:1 mixture of potting soil to sand with some peat moss. The soil should be moist, not soggy, before mixing and adding to the container. Avoid using soil from your yard or soil that has not been sterilized since it may contain soil pathogens can easily impact plants in a terrarium environment.

Carefully inspect all of the plants for signs of insects or disease before planting them in the container. When planting, be sure to leave plants enough room to grow without crowding each other. Cover plant roots in the soil and moisten the area with water. Place the covered terrarium in an area where it will receive bright light, but not direct sunlight. Bog terrariums should be kept in a cool area, whereas woodland and desert terrariums can be kept at room temperature.

The first few weeks of maintaining a proper moisture level in the terrarium can be tricky and is often the demise of a well-planned terrarium project. Planting medium should be kept moist, but not soggy. Standing water is difficult to remove from a terrarium and can quickly lead to root rot, mold and other problems. Some moisture on the walls of the container can be expected, but a dense fog indicates over watering, and you should remove the cover so some water can evaporate.

For more information about building a terrarium, a complete list of suitable terrarium plants and troubleshooting, call the Rutgers Master Gardener Helpline at 908-788-1735 Mondays and Wednesdays from 10 am to 12 pm and Tuesdays and Thursdays from 1 pm to 3 pm, or stop by the Rutgers Cooperative Extension office located off Rte 31, just north of the Hunterdon Medical Center.