How to Plant a Terrarium
If you can’t wait until the weather warms to get your hands in the soil, why not stretch your green thumb indoors by planting a terrarium? Gardeners have enjoyed tinkering with tiny terrarium plants for thousands of years, beginning with the ancient Greeks. They started the trend of planting these miniature gardens so they could bring a bit of the natural world inside.
A true terrarium is a small indoor garden that’s planted in a tightly closed transparent container. Plants in terrariums need watering less often than typical houseplants because the container traps moist air inside. Terrariums can be open containers, too, but these require a more regular watering schedule.
Any clear glass or plastic container can be turned into a terrarium. There are specially-designed, ornamental terrariums that look like doll-sized Victorian greenhouses or you can use any large glass or plastic bottle, one-gallon Mason jar, goldfish bowl, recycled fish aquarium, old glass coffee pot, brandy snifter or other creative options. Finding the right container is part of the fun.
If you’re starting with your first terrarium, look for a container with a large opening to make planting easier. Those more experienced with planting terrariums test their skill using deeper containers with smaller openings and improvising special long-handled tools for planting.
Once you find the perfect container, clean it thoroughly. Wash with hot soapy water, rinse and allow to dry. Then you’ll need to use a spoon or trowel to place several layers of material on the bottom of the container to allow for drainage. The drainage material and growing medium usually take up about one-quarter of the container.
The recommended bottom layer is about one-inch of gravel, followed by a half-inch layer of activated or horticultural charcoal. The charcoal helps remove toxins and harmful chemicals to keep plants healthy, plus it absorbs odors. Cover the layer of charcoal with sphagnum moss to keep the growing medium from mixing with the drainage area.
If you skip the charcoal layer, be sure to add a thicker layer of gravel to make up for the lack of charcoal. Use distilled water for watering plants to avoid the chemicals in treated tap water. You can also remove the lid from your terrarium to allow air to circulate several hours every day. The terrarium may need slightly more watering with this method.
Another alternative to charcoal is to replace that layer with a layer of live moss. If you use moss, be sure to give it some air by opening the terrarium for a few hours daily.
The growing medium is the next layer. Purchase a packaged soilless potting mix that’s made up of peat moss, vermiculite and perlite or use a sterile potting soil. Moisten the mix slightly before adding about 1 to 2 inches to the container.
Now decide how you’ll display the container. Will it be seen from one side, two sides or all sides? Knowing how you’ll enjoy looking at the terrarium will help you with planting. If the view is from the front, place taller plants in the back and smaller ones in front; if you want to see the garden from all sides, place taller plants in the middle surrounded by smaller, low-growing plants.
Selecting plants for your terrarium is as important as selecting plants for your landscape. Look for plants in different sizes and textures that have similar needs for light, temperature, and water. Avoid mixing plants with extremely different needs such as planting a cactus with tropical plants. Think about planting one special or unusual plant as a focal point, just as you would outside.
There are many attractive terrarium plants on the market, so you can create the kind of indoor garden that matches your taste. Look for plants that like a moist environment, like tiny ferns, baby maidenhair, sedums and mosses, just to name a few. Plants sold for use in fairy gardens are perfect for terrariums, too.
Before planting, arrange the plants in an area similar in size to your container. It’s easier to move plants around while you’re thinking about placement, than it is to move them after planting.
When you’re ready to plant, trim damaged or yellowed leaves, remove each plant from its container, brush off excess soil, and place roots in the growing medium. Keep plants away from the sides of the container so they won’t be touching the glass.
Fill in the planting hole with the potting mix and tamp it down a bit. Take your time and continue planting until you’re pleased with the final result. Add other decorative items to the terrarium, such as polished stones, bark, ceramic woodland critters or other embellishments.
Use a mister to gently mist all the foliage and growing medium; leave the lid off the terrarium for a day. Then mist again, allow leaves to dry and cover. Keep an eye on the terrarium over the next week to make sure there’s enough moisture, and add a small amount of water if you see signs of wilting.
Once planted, your miniature indoor garden should give you as much pleasure as your outdoor garden, without any heavy lifting.
How to Care for a Terrarium
Your terrarium garden is meant to be easy to care for, especially if it has good drainage and a clear tight-fitting cover.
During the first few weeks after planting, look for signs of leaf wilt or decay and remove sick plants to keep from spreading problems to other plants. While fungal diseases can be an issue, the most common problem in terrariums is root rot from too much standing water.
Here are the best practices for caring for your terrarium garden:
Light The typical light needed by houseplants works for terrarium plants, too. Place the terrarium near a window so it gets good, indirect light. Because of the enclosed environment, plants will burn if placed in direct sunlight.
If the light is too low to encourage healthy plants, you may need to supplement with artificial lighting. If plants begin to lean in the direction of the light, turn the container.
Temperature Most terrarium plants are either woodland or tropical plants. Keep your plants’ natural environment in mind when it comes to temperature. Most plants will do well in household temperatures that range between 65-75 degrees. If you’ve planted your terrarium with woodland plants, you may want to place the container in a cooler location of the house.
Water A light misting may be enough to keep plants healthy in an enclosed environment. If you notice a lack of condensation inside the container, or that plants are wilting, then you know it’s time to add a small amount of water. It’s better to keep the terrarium on the dry side, especially the foliage. Overwatering is the number one cause of houseplant decline, whether in or out of a terrarium.
If water splashes on the glass creating unsightly spots, you can carefully clean the glass with a small piece of wet sponge attached to a sturdy piece of wire.
Fertilizer A light fertilizing with a houseplant fertilizer may be needed only occasionally, especially if you used a soilless planting mix that has no natural fertility. Fertilize lightly once plants are established just to keep them healthy. Too much fertilizer will cause the plants to outgrow the container.
Pruning When terrarium plants outgrow their space, they’ll need pruning. Trim with long scissors or use your fingers to pinch tips before plants grow too tall. Be sure to remove any trimmed leaves from the bottom of the terrarium.
Replacing plants If a plant should die, remove it quickly and replace with a healthy plant.
By their nature, enclosed terrariums are designed to be relatively maintenance free. Your terrarium should give you many years of enjoyable indoor gardening if you remember to keep the container out of direct sunlight and give it just a little bit of water when the growing medium starts to dry.