The herb gardener who is homebound by winter can take
pleasure in a different kind of garden environment: an ecosystem in miniature whose tiny plants are seen through the glimmer of glass.
When a small garden in a closed or nearly closed terrarium thrives, the gardener knows it has found a proper balance of the elements of its survival–air, light, moisture, humidity, and soil. Moisture evaporating from the plants’ leaves condenses on the container walls and runs down into the soil, where it is taken up again by the plant and utilized in an ongoing cycle. Putting together an ornamental tabletop terrarium can be a thought-provoking, satisfying project when the wind outside is howling.
For herbs that might do well in such an environment, we looked to moisture-loving woodland natives such as foamflower and ebony spleenwort, as well as low-growing old favorites such as violets and sweet woodruff. Most of the familiar culinary herbs would meet certain death in a terrarium because of its dim light, high humidity, and lack of drainage, although some will grow in an open dish garden. Like a terrarium, a dish garden has no drainage, but it can be placed in direct natural or artificial light. See the chart on page 37 for other herb options.
Many containers can become terrariums; consider using an old aquarium or goldfish bowl, an old-fashioned cloche with a dish for it to rest on, or a large brandy snifter. The Victorian-looking teardrop terrarium on page 34 is not suitable for growing edible plants because it is made of leaded glass, but it sets a mood beautifully.
Making A Terrarium
Choose a clear glass or plastic container with a large opening, or one whose top can be removed, such as a 10-gallon fish tank. The container must be scrupulously clean to minimize the risk of plant disease.
Look for plants with similar requirements in humidity, light, soil, and water. Plant a woodland terrarium with plants from our chart on page 37, or a desert terrarium with aloes and cacti; the latter would need virtually no water. A tropical terrarium must be kept warmer than a woodland container, and plants for a bog terrarium can tolerate wet soil.
Select plants in a variety of heights, textures, and leaf sizes and colors. Seek out miniatures and slow growers, as many as twelve plants for a 12-inch container. Too many plants, however, can make the terrarium look cluttered.
Mix together three parts sterilized dry commercial potting soil and one part crushed charcoal. Fill the container a quarter full with this planting medium, keeping the walls clean. Create a little scene in the terrarium, complete with hills, valleys, and rock boulders. If you want, add a small statue or piece of driftwood just for fun.
Decide the arrangement of your plants in the container. Plan to place taller plants toward the back and slightly off center, and fill in with smaller ones; keep in mind blending and contrasting foliage colors. Dig planting holes. Knock the plants out of their pots and loosen the roots. Place each plant in its hole, firming the soil mix around the roots. Don’t let the foliage touch the glass.
Add water very sparingly down the side of the container (there’s no drainage, remember). Use tap water that has stood overnight to eliminate chlorine. Cover the terrarium and set it in indirect light. If a lot of moisture appears on the glass soon, remove the cover for a few hours, then cover and observe again. If you see standing water in the container, remove it with a turkey baster.
Although direct sunlight falling on a terrarium can steam the plants to death, overwatering is probably the leading cause of failure. Water only when the soil feels dry. Because slow growth is desired, feed plants sparingly with diluted houseplant fertilizer.
Remove dead leaves and faded flowers to prevent disease, and evaluate the terrarium’s general appearance occasionally. Leggy or spindly plants need more light; brown leaf tips or yellow leaves indicate too much moisture. Move overly vigorous plants to another location. Hand-pick insects if possible, but if bug invasions and mildew attacks are severe, you probably need to start over with a clean terrarium and new plants.