Tam-Tam's Blog

Terrarium Maintenance
Jan 23, 2008 | 5:50 PM PST
Tags: terrarium , maintenance , pruning

The theory is, with the ideal conditions met, the average plant could survive in a terrarium for up to fifty years without attention.  This means you would have to have the ideal growing medium, the ideal amount of light, and a constant ideal temperature.  Chances are that any given terrarium may have one or more of these conditions that are out of sync with the "ideal" recommendation.  So if you decide to become a glass gardener, realize that varying degrees of maintenance will be involved. 

Moisture:
Possible signs of insufficient moisture:  no condensation on the walls of the container.  Plants are drooping.  The foliage is becoming brittle.  Dried up moss or parched-looking soil.

Possible signs of too much moisture:  Decaying foliage and plant rot.  Extremely heavy "rain clouds" on the container walls.  Remember, too much sunlight can cause excessive condensation to form.

If you have a tank style terrarium, you can check the moisture level by feeling the soil about one inch below the surface.  Although there is no real way to accurately check the moisture in narrow-neck containers, experienced glass gardeners say they can tell by the weight of the narrow-necked containers.  If the container seems light, they add water with a hand sprinkler or a long spouted watering can.

Light:
If you are using natural light for your glass garden, keep in mind that the amount of light the terrarium receives can change at any given time, especially with the seasons.  This means that vegetation can get too much sunlight at times and not enough at others.

If the leaves of the foliage turns yellow or look "burnt", this may be signs of too much sunlight. On the other hand, if the blossoms on flowering vegetation seem to retard, this may be a sign of insufficient light.

If the terrarium is exposed to too much light, it needs to be moved to a shadier spot, or sheltered from the direct light or the heat from the spotlights.  Sometimes the intensity of the sunlight is less in the wintertime months and the terrarium may need to be moved to a sunnier location or provided with the aid of artificial light.

Unless the terrarium plantings are receiving evenly distributed light from an overhead light source, the terrarium vegetation may experience tropism.  This means that the plants will twist and lean toward the light source.  If your cylindrical containers are experiencing tropism, you can turn the container a half turn.  For oblong (tank) containers you can turn them completely around.  When the plants straighten up, (may take a day or two) you can turn them back to their normal positions.

Pruning:
Keep in mind that you want the soil to have just enough nutrients for slow steady growth in the terrarium.  If the soil is too fertile it causes lush, rampant growth that takes over the design elements of the garden.  Extra growth can be kept in check by pruning the overgrown branches and excess foliage, or removing the plant once it has become too large for the container.  Make sure you know how each plant will need to be pruned because some plants can be killed by cutting the tops off, while others like spreading plants can be kept in check by removing unwanted growth.  Removing fading or spent blossoms, yellowing or dead leaves and stems, and side shoots helps to maintain the beauty of your glass garden.

When trimming plants in a wide mouth container you can use grabbers or tongs to hold the plant while using the pruning shears made from the wooden dowel with the razor blade, to cut away overgrowth and unsightly foliage.  Then use the grabbers or tongs to remove the pruned material.  Narrow-neck containers are usually to difficult to prune, thus it is usually easier to just reconstruct the entire planting.

Pruning Tips: 
Trailing plants like ivies can be pruned by simply shearing off unwanted growth. Strawberry begonias and other plants that send out runners can be pruned by cutting off the offshoots.
Cutting the tops off of coleus and impatiens can stimulate growth along the main stem.
Pruning a fern by slicing some of the outside fronds (leaves) below the soil line with a single edge razor blade will encourage additional new, low growth.  One of the best ways to trim a fern is to remove the plant from the container and separate it into smaller individual plants.  If you plan on trimming the outside fronds make sure to do it a little at a time, otherwise you may injure the plant.

Insects:
Your first thought may be that the plants in a terrarium will be protected from insects.  This is true, that is if there are no hitch-hikers.  Harmful pest can hide in the root ball of potted plants and live moss may be hiding eggs of harmful species, especially if the moss is collected from woodland areas.

Try spraying the plants with a houseplant insecticide before planting them in the terrarium, making sure to follow the directions.  It may seem neat to watch these little critters in the terrarium, but remember, these pests will strip down and destroy your glass garden in no time.  As soon as you see an insect in the terrarium, you should spray the plant(s) with a general-purpose insecticide.  Make sure to follow the directions for the insecticide you are using and be careful of over spraying the plants. 

Don't forget to remove all traces of the spray from the inside walls as soon as possible.  Depending on the size of the container, you may be able to place pieces of paper against the wall of the container to help with overspray.  The walls of a narrow-neck container may be cleaned off with a piece of lint free cloth wrapped around the end of a dowel and fastened with a rubber-band.

Make sure to leave the cover off the container after spraying, to allow the fumes to evaporate.  It may take several applications sprayed three or four times at weekly intervals to get rid of pest infestations such as whiteflies.

Mold:
The humidity in the terrarium provides an ideal environment for mold.  Mold is the most common disease that glass gardeners have to deal with.  The wooly looking growth that spreads over the soil is produced by a variety of gray fungus.  Although the mold may be due to an infected plant, the usual case is too much moisture.  Mold will develop very quickly and will destroy a planting in a very short time.

Hopefully, removing the infected plant will stop the growth of mold.  Make sure to properly destroy the infected plant and that it does not come in contact with the new plant that will replace it.  If needed, dust the garden with a general-purpose fungicide being sure to follow the directions.  If the dusting does not alleviate the situation, the terrarium must be dismantled and replanted.

There is no guarantee, but...
hopefully with regular maintenance your terrarium will function properly for a long time.  But as you can see, sometimes things go wrong.  Maybe the plants are growing to fast and need to be replaced, or there is some kind of problem that makes it necessary to just empty the container, wash it out and start all over.  Try not to let this get you down or frustrated. Like any other form of gardening, learning how to do it is part of the fun.  Good Luck!

Next up:  Other stuff you can do with a terrarium.