Building a terrarium is a fun activity for gardeners of all ages and is sure to cure the cabin fever that is setting in with the colder weather and short days.

All you need is a clear glass or plastic bottle, jar or similar container to get started.

The basic idea of a terrarium is to create an environment where plants can live without human care. That’s right — you build it and then sit back and enjoy the beauty for years to come. If the terrarium is open, like an aquarium, it will need a little maintenance and care but it should still require less attention than the typical houseplant in a pot.

The terrarium container can be open or closed — I have used clear 2-liter plastic bottles for the most basic terrarium environment. An old aquarium, like I mentioned, could be used. Some of the prettiest terrariums I have seen are in very large glass bottles — either upright or sometimes turned on their sides.

Once you have a container, you will need potting media, pea gravel or a similar material, activated charcoal, sphagnum moss, and plants. You might also wish to create a theme — such as a woodland or desert — and select a few accessories to go with the theme. Woodland themes are generally the most popular look for terrariums, and you might add a small piece of wood or other natural materials to accentuate the look.

For potting media, use a commercially blended soilless mix for best results. Bags that are labeled garden soil or topsoil are less desirable for container-grown plants.

If the container is mostly enclosed, like a bottle with a narrow opening, you will also want a few tools. Quarter-inch diameter dowel rods can be used to dig holes to set plants, and a dowel with a looped piece of wire in the end works to set plants into place. A spoon and funnel can be handy to put the potting media and drainage material into place.

When you are ready to put it together, start with the pea gravel or drainage material of choice. This is an area where water can collect before it evaporates to rain back down on the plants. Cover the entire bottom of the container and make sure the material is deep enough for it to do its job. In simple two-liter bottle terrariums, I use perlite instead of gravel.

Place a 1/2-inch layer of activated charcoal on top of the pea gravel or pebbles. The charcoal is a filtering agent and is more important in closed terrariums than open ones.

On top of the activated charcoal, spread a thin layer of sphagnum moss. This is just to keep the potting media from moving down into the charcoal and gravel.

Next you are ready for potting media. Moisten it if it is very dry, but avoid drenching it. Add it in a layer on top of the other materials. The depth can depend on the size of the container, but add at least 1 1/2 inches of potting media for any plants to give room for root growth.

Use the dowels and/or stick and loop to transplant plants into the container. Keep leaves from touching the sides of the container if possible, and give the plants a little room to grow. Use a squirt bottle to rinse soil from plant leaves and stems if any has gotten displaced. You can add a little water, but be careful not to overwater since moisture is unable to escape in an enclosed system.

Once the plants are in place, add any other items you want in the terrarium.

Watch the terrarium the first few days to make sure the moisture level is appropriate. If it is a closed container, leave the lid off those first few days or longer if plant leaves are remaining wet. When the system works, water will condensate on the ceiling of the terrarium and rain on the plants, so more water is unnecessary. Even in a mostly open system, you might only add water once every three or four months.

Fertilizer is also generally unnecessary as it is usually in the potting media. After a year or so, you may wish to add a little water-soluble houseplant fertilizer.

Location depends on the type of plants in your terrarium (hopefully you selected those based on where you planned to put the terrarium). Just avoid putting a terrarium in direct sunlight because it can warm up like a greenhouse and cook the poor little plants inside.

For plant selection, check with your local garden center for recommendations or download the University of Missouri Outreach and Extension publication “Terrariums” from its website. The guide also contains information about pruning plants and long-term care of terrariums.

Then you can sit back and enjoy watching the plants grow!

— Jennifer Smith is the Horticulture Extension Agent for K-State Research and Extension in Douglas County. Contact her or an Extension Master Gardener with your gardening questions at 843-7058 or dgemg@sunflower.com.