Clippings
A weekly column about plants, yards & gardens
By: Margaret Murphy, Horticulture Educator, Lyon-O’Brien-Osceola-Sioux Counties
ISU Extension & Outreach
Gardening Under Glass
Keeping with the theme of indoor plants, this week’s column is about terrariums. Growing plants
in a clear glass or plastic container dates back to the mid-1800s. The idea came about from the practice
of transporting plants in a sealed, glass box known as a Wardian case. It was designed by an English
botany enthusiast who needed a way to protect live specimens as they were being shipped from foreign
lands back to the British Isles. The attractive look of these enclosed plant houses was quickly adapted for
use in home decorating.
In a terrarium, the plant takes up water from the soil and through transpiration releases water
back out into the container. The water condenses on the glass which then trickles down into the soil
where it is again available to be taken up by the plant roots. This cycling of moisture creates a very
humid environment ideal for tropical plants. It also greatly reduces the need for watering, which is great
for gardeners, such as me, who sometimes forget to regularly water their indoor plants.
Terrariums can have either an open top or be covered. You can purchase glass containers
designed to be used for a terrarium or convert an old glass or plastic container such as a fish bowl, water
pitcher, or large jar. Make sure the container that you use is clean. Wash with hot, soapy water and rinse
thoroughly, or run it through the dishwasher. Finding an encasement that easily fits your hand will make
things easier; however, for smaller openings you can enlist the aid of tools such as a large kitchen spoon
or tongs to get the plants set in the soil.
Since terrariums do not have drainage holes, a drainage layer needs to be created. Start with a
couple of inches of gravel, rocks or perlite on the bottom of the container. Colored rocks or pebbles can
add interest to a design. Add ¼ to ½ inch of horticulture charcoal. This helps with both drainage and
controlling odors. Placing a layer of sphagnum moss on top of the charcoal can prevent soil from filtering
down into the drainage layer. Lastly, add a few inches of light potting soil. This should be a well-draining
soil mixture. You can blend your own using equal parts of soil, peat moss, and vermiculite, or use a
commercial mix such as one made for African violets. There is no need to add fertilizer. It is easier to
maintain the terrarium with plants that do not grow too rapidly.
When creating your encased garden, remember that the terrarium environment is high in
humidity. Choose plants that like humid conditions. Also select varieties that thrive in low light. Direct
sunlight may burn your plants so keep a terrarium under florescent lights or near a window that receives
indirect light. Check the plants to make sure they are disease and insect free as both will flourish in a
terrarium environment. A few plants that typically do well in terrariums include: creeping fig, ribbon
plant, earth star, prayer plant, creeping moss, table ferns, strawberry begonia, parlor palm, African
violet, English Ivy, peacock plant, and Bromeliads.
How to arrange the plants in a terrarium does not differ much from how you would design a
regular container. You can follow the established recipe of using a tall, focal plant surrounded by a few
medium-sized fillers or a ground cover. Decide whether the terrarium will be viewed from all sides or
just from one direction. With one that needs to look good from all angles, it is common to accent the
landscape with a mound or hill. For containers where you are building the design from back to front, you
might consider a sloping landscape. Once the landscape and plants are set, terrariums are sometimes
decorated with shells, driftwood or toys. You can make a mini jungle with wild animal figurines or craft a
prehistoric setting with a couple of little, plastic dinosaurs.
Though fairly self-sufficient, a terrarium does require some care. Water an open top terrarium
when the soil looks dry. Water lightly as it is better to have conditions be a bit drier than too wet.
Covered containers may require watering only once every several weeks, or in some cases, months. If
your terrarium develops standing water or you notice rotting plants, take the cover off for a few hours a
day until the excess water evaporates. Remove spent flowers and dead leaves and trim back any
overgrowth. If after a time plants appear to lack vigor, you can give them a very light application of
water-soluble fertilizer.
Terrariums are a wonderful way to create a fun and interesting indoor garden. It is also a great
project for kids. Please feel free to contact me with any questions at my email [email protected],
by phone at (712) 472-2576 or through your local county Extension office.