Cheyenne Garden Gossip

Gardening on the high plains of southeastern Wyoming


Terrarium techniques

2020-02 Denver BotGarden-Edwardian case

This early type of terrarium, photographed at the Denver Botanic Gardens, is known as a Wardian case. In the 19th century it protected plants brought from exotic locations.

Published Feb. 23, 2020, in the Wyoming Tribune Eagle, “The terrarium: A little world at your command”

By Barb Gorges

Planting a terrarium sounded like a good way to get my hands in dirt mid-winter and protect tasty houseplants from marauding kittens.

The concept is simple: a glass container with potting soil and plants. Plants that enjoy humidity grow in a closed container. Plants that like a dry climate, like succulents and cacti, are in open, but high-sided containers.

Closed terrariums, once you get the moisture level right, can putter along for weeks on their own—perfect for busy people and frequent travelers.

Sometimes a terrarium features just one plant. More often, a miniature landscape is created. The watery corollary is the single goldfish in a bowl compared to an aquarium complete with multiple fish, aquatic plants and decorative elements. Empty fishbowls and aquariums can become terrariums.

Laramie County Master Gardener Susie Heller offered me advice based on her extensive experience. Her terrariums are scattered all over her house and range from clear glass bulb-shaped hanging ornaments to a 5-gallon clear plastic water bottle. Her most recent project was a basket she lined with plastic fabric, planted and then topped with a clear plastic hood.

Inspired by Susie’s stories of finds at vintage and thrift stores, I checked out Goodwill and for only $2, came home with a 4-inch-diameter glass food storage container with a glass lid that clamped on.

Susie uses sand or pebbles for the bottom layer of the terrarium. Excess water in a normal pot drains away, but in the closed terrarium system, roots would rot in excess water if it didn’t collect below the soil level.

The WikiHow article I read suggests digging up some gravel from your driveway. Mine’s concrete and I didn’t have sand like Susie uses, so I went to the pet store’s aquarium section. They have a huge selection of gravel of different sizes and colors. I decided against hot pink. My selection, a 5-pound bag of fine, golden-brown gravel, was $6.  I poured a layer in the bottom of the container. Figure half an inch for small ones, up to 2 inches deep for large former aquariums.

The WikiHow article suggested a layer of activated charcoal next to keep things smelling sweet. This is not charcoal briquettes. But it is the same as activated carbon sold for aquariums. I bought a jar of small pellets for $11. A thin layer is all that is necessary—plenty left for future terrariums.

Next, potting soil. I always have a bag of the peaty stuff around. If I were planting succulents and cacti, I would look for the sandy potting soil they require. WikiHow suggested digging up some dirt from outside but it’s frozen this time of year, mine is clay-like anyway, and I don’t want to have to bake it to sterilize it—it smells up the house.

I moistened my peaty potting soil in an old dishpan before putting it in the container. It comes dry and is hydrophobic when I first pour water on it, so I give it a few minutes to soak.

How much soil do you add? That depends on the size of the container and the plants you want to grow. But on the other hand, plants in a terrarium don’t need the soil depth they get in a pot. Aesthetically, you want the drainage material and soil to be one-third or less of the height of the container. You can trim long roots or, after putting in most of the soil over the charcoal, spread the roots out and cover with more soil.

2020-02Terrarium 1            Picking the plants was the toughest part of the project. Susie said the plants in one container should all have the same moisture and light requirements. I found three small tropical houseplants ($4 each) at the store with labels indicating they all shared the same levels. I also had cuttings at home I thought might work.

Most of my plants were too big for the Goodwill container, and even the two other containers I found in my basement, a 7-inch diameter glass cookie jar and a 6-inch diameter 1-gallon pickle jar. The leaves aren’t supposed to touch the glass. Pruning helps. And if you didn’t select slow-growing plants, you’ll soon be pruning anyway.

Susie adds moss and interesting trinkets to the soil surface of her tropical dioramas. I found some stones outside and some twigs and bark from the woodpile. The half-decayed twigs sprouted fungus within two days, so I took them out.

Some of Susie’s terrariums have narrow openings and she has MacGyvered long-handled implements to help place plants and objects.

The last steps are to wipe clean the inside of the glass, put the lid on and put the terrarium near light: either window, grow-light or fluorescent light. It will take a little experimenting to determine how much light each of my new jars of plants prefers.

Moisture is easier to control. If the glass steams up, I leave the lid ajar for a day. If the soil gets dry, I will mist the plants.

I will strive to be benevolent master of these small universes I have created.

2020-02 Terrarium 2