The Plant Lady: Wash away the winter grays with a sunny terrarium

When the weather turns gloomy and outside garden chores are minimal, my thoughts often turn to inside plants. One of my favorite ways to grow houseplants is in terrariums. Besides being beautiful they are ideal for homes with young kids or pets that tend to destroy or nibble on houseplants. Bonus – completed setups or the “ingredients” to make one are great holiday gifts for adults as well as kids.

Almost any clear, watertight container can be turned into a terrarium. Many people choose to use an old fish tank due to their size and commonality. Thrift stores are a good place to find used ones. I find that discount home stores are a good source of glassware with lids. But in lieu of this even a clear plastic jar will suffice. At home I have an old jewelry display case repurposed into a coffee table terrarium, so use your imagination. Minimum height should be 8 inches, but the taller/wider it is, the more variety of plant material you can grow. Some terrariums can be quite involved with waterfall features and tree structures.

Most of the directions for terrariums will recommend placing a layer of gravel on the bottom, followed by a layer of horticultural charcoal (not BBQ charcoal which contains many chemicals hazardous to plants) and then the soil. The idea behind the charcoal is that it will absorb moisture and the smells associated with stagnant water. I bypass the first two layers with no negative effects. With correct watering, the need for charcoal is negated and gravel does nothing but reduce the amount of root space. My go-to soil substrate at home and at the UC Davis Botanical Conservatory is equal parts peat moss, small perlite and horticultural sand. This soil holds a good amount of moisture, but the perlite and sand allow for aeration.

When planting, choose humidity-loving plants that will stay small. When possible, I prefer to start with cuttings. The environment of a terrarium is basically a greenhouse, and as such, roots form quickly. Following is a list of plants that are ideal for a terrarium. Most of these (and many more) can be found at online nurseries specializing in terrariums or even your local nursery. Flori-Culture is a great local resource that not only has terrarium plants, but also all hardware needed to start one.

Terrarium all-stars

Geogenanthus poepegii, Peperomia caperata, Philodendron brandtianum, Selaginella, Fittonia, Cryptanthus bivittatus, Macodes, Begonia soli-mutata, Begonia prismatocarpa, Pellionia repens, Pilea glauca, Peperomia prostrata, Mediocalcar decoratum

Besides a tropical terrarium, carnivorous plants can be used either mixed in with tropical plants or in their own container. These are plants that rely on dissolving insects to obtain nutrients. Not all are ideal for a terrarium, but those which will work are Drosera (sundews), some species of Nepenthes and Pinguiculas (butterworts). The same soil mix mentioned previously is recommended for carnivores. Be extra careful with the water quality on these plants as they require water with no nutrients and no fertilizer.

Directly after planting add water. You are aiming for slight condensation on the sides of the container. After adding water and sealing up your terrarium, check back in about an hour. If you have added too much and water is running down the sides, simply open the lid and let some of the moisture escape. If so much water has been added that it is pooling at the bottom then a turkey baster is a good way to get water out. If no condensation is noticeable then add water until this occurs. An optimal operating terrarium should only need water added every several months at most. If you have hard or chlorinated water, then use bottled or reverse osmosis water.

Your terrarium should be kept in a bright but indirect light location terrariums – an east-facing window is ideal. If near a south or west window, ensure it is several feet away, especially in spring/fall, as a closed container can heat up quite a bit. Avoid close proximity to heater vents as well. Supplemental light can be used if growing in a dim lit location. For this, aquarium LED lights or even a fluorescent light will work well.

Some plants can get larger than desired. Simply prune these back. Sometimes, plants have to be removed if getting too large. To safely remove them without destroying the surrounding plant, I like to use small pruners to cut the root ball out. If plants are yellowing (and you know you are not overwatering) then it most likely is time to fertilize. Generally abundant fertilizer is not needed, but giving a bit of houseplant food every few months will keep your plants happy. Remember that fertilizer is a salt and in a terrarium the salt cannot be flushed out – so go easy on the quantity and frequency.

This story was originally published December 10, 2019 at 10:51 AM.