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How to Create a Terrarium Garden

November 27, 1999
When summer becomes nothing more than a memory, and the garden has gone to sleep for the winter, many gardeners revert to 'indoor mode'. While caring for house plants is somewhat satisfying, a potted plant sitting alone, on a table is just not the same as a garden filled with flowers.

The Terrarium Concept

A terrarium is a collection of compatible plants grown in an enclosed, or partially enclosed, clear container.
Creating a terrarium filled with ferns and other small plants is a practical and fun way to have a miniature landscape inside your home. Their easy care is ideal for people who are too busy to spend a lot of time caring for plants.
Your choice of containers is only as broad as your imagination.
There are many ready made terrariums available, or you can use bottles, jars, aquariums, fishbowls, or even brandy snifters.Get creative!
Terrariums allow you to grow plants which require a high degree of humidity, which otherwise would probably perish in the dry atmosphere of a heated home.
Once the plants become established within your miniature garden, the terrarium begins to create a climate of its own.
The plants transpire moisture through their leaves, which then condenses on the glass, and flows back to the soil.
This 'rain effect' allows the terrarium to go for weeks without watering.
Terrariums should never be grown in FULL sun!
For your new terrarium to succeed, it is extremely important that it is properly set up.
As with any landscaping project, selecting appropriate terrarium plants is also very important.
Terrarium plants need to be compact, and slow growing, as well as being able to survive the same conditions as their companion plants.
To avoid insect and disease problems, be sure to only use a good quality, commercial potting soil which has been pasteurized to kill any organisms which may be present.
Additional planting materials, like the rock you will use for drainage, and stones or driftwood you use for landscaping accents should be rinsed with clean, HOT water, before using.
Inspect the plants you are using, very carefully, for signs of insects or disease, or any other potential problems.
For the beginner, I recommend that you choose a large, open container such as an aquarium. These are much easier to work in. With experience, you can advance to using 'chopsticks' and dibble sticks to plant your garden inside a small mouthed container, much like building a 'ship in a bottle'.

Set up Your Terrarium Environment

Before you begin construction, get all of your tools, materials, plants, and of course your container, together in one convenient place.
Your planting foundation will consist of four layers.
  • The bottom layer is for drainage, and consists of pea gravel, pebbles, or very coarse sand.
    Proper drainage is essential to ensure that the soil doesn't become over-saturated, which may lead to root rot, and the death of your plants.
    Depending on the size of your container, you will want to spread at least an inch of drainage material evenly across the entire bottom of your terrarium. For large or deep containers, up to 3 inches of material may be used.
  • On top of the drainage layer, it is a good idea to spread a thin layer of activated charcoal, like you would use in your aquarium filter.
    This layer will help to clean the air of the fumes caused when the organic materials begin to decompose.
  • The third layer is a thin cover of sphagnum moss, spread evenly over the first two layers.
    The purpose of this, is to prevent the soil from sifting down into the drainage layer, which would render it useless.
  • The final level is that of your soil. Many garden centers sell a potting mix specifically for terrariums. In reality, all that you normally get for the extra money is sand added to their regular potting mix. You may choose a pre-mixed terrarium soil, or if you prefer, just add one part coarse builders sand, and one part leaf mold (or humus) to each two parts of your usual mix.
    Never use beach sand in any potting mix!
    Do not add any fertilizer to the terrarium mix. It already has enough nutrients to last a long time. Too much fertilizer will cause the plants to out grow their surroundings much too quickly.
  • If your intent is to create a desert type terrarium garden, be sure to add extra sand to the soil mixture, and additional gravel to the drainage level.

Creating Your Terrarium Landscape

While the bottom tree layers are laid in evenly, the terrarium will seem more realistic if you add contour to the landscape, with different levels of soil.
You can create terraces, valleys, and hills.
Use your own special stones or pieces of wood as landscape accents, just as you would use driftwood or boulders in your outdoor landscape. Use your imagination.
The main difference in this case is that you must miniaturize everything you do.
If you intend to add critters of any kind (like lizards or tarantulas) to your terrarium, be sure to create a 'lake' somewhere within the landscape for them to drink from. This can be made out of any shallow dish or saucer, depressed into the soil.
Your terrarium plants should be chosen for their compatibility in lighting, watering, and humidity needs. Choose plants of varying height, shape, texture and color to create the desired landscape effect.
Small specimens of plant varieties that do not grow too quickly are your best choice.

Adding Suitable Terrarium Plants to Your Garden

Once your decision is made as to where you will set your terrarium up, and you have chosen the appropriate plants, you are ready to go to work. Your new landscape should be structured and set up for the best visual effect from the viewers point of view. For example, if the garden will be viewed from all sides, a large plant should be planted in the middle, with lower plants around it. If your terrarium will primarily be viewed from only one side, the tallest plant should be placed near the rear of the container, with lower plants in the foreground.
It is sometimes a good idea to use something special as a focal point in the landscape, such as a rock or stick to simulate boulders or logs. In these cases, or if you should decide to include a small statue as part of the garden, be sure that it is about the same scale as the plantings.
Before you do any planting, take your time and make certain that the arrangement of your plants creates the desired effect. While they are still in their pots, set the plants around inside the terrarium. In narrow mouthed containers, it is a better idea to put your ideas down on paper. Adjust the soil level to create hills at the back, and valleys in the foreground. Move your logs and boulders to different locations within the landscape. Step back a foot or two and see if your arrangement creates the desired effect. If not, do a little more rearranging, and check it again. When you decide that you have created the right 'scene', you are ready to do your planting. No special tools are needed for planting your terrarium, unless you are using a bottle or other narrow mouthed containers. Most likely, you will use a kitchen spoon as your shovel, a fork as your rake, and small scissors as your shears. Narrow-mouthed terrariums require special tools to get the plant down into the terrariumand into the right spot. (i.e. a funnel to add the soil, long slender sticks to dig with, and some type of 'grabber' (unless you are good with chopsticks) to lower the plants in, and to actually plant them. Once you have determined the arrangement of the plants and terrain, you are ready to landscape.
Remove the plant from it's pot, and set it into a pre-dug hole.
Unlike planting in the garden, it is not necessary to loosen the plant's roots. In a terrarium, you don't want the plants to grow too quickly, and leaving the root ball compacted will slow the growth of the plants.
Firm the soil gently around the roots. Do not crowd the plants or place them directly against the sides of the container. Allow sufficient space for them to grow and spread, without becoming entangled in other plants.
After planting, the soil should be slightly moistened.
Never allow the soil to be soggy, unless you are growing 'Bog' plants!
A lid should then be placed on your terrarium.
Normally, a clear sheet of glass is used, but you may have to use your imagination to find the appropriate lid.

Terrarium Maintenance

Check the terrarium frequently for the appearance of condensation on the glass.
If large water drops appear on the glass, the container should be left open for a while, until any excess moisture evaporates. In some cases, it may be necessary to keep the lid slightly opened, to allow for fresh air circulation.
However, keep in mind that a balanced terrarium should have a certain amount of moisture on the glass.
A completely enclosed terrarium requires little or no watering. If it is not totally enclosed, you may have to water on a weekly or monthly basis (more often for completely open terrariums or dish gardens).
The addition of water only becomes necessary if no condensation accumulates on the glass. When water is eventually needed, it should only be added a small amount at a time, since there is no place for the surplus water to run off.
Over watering quickly increases the danger of fungus or mold.
Recheck the next day, and if no condensation has appeared, more water may be added.
When in doubt, always water less, but watch carefully so that plants do not become too dry and wilt.
Generally, terrariums should not need fertilizing, but if the plants start to appear malnourished, you may feed them using a very weak mixture (1/4 strength) of an all purpose house plant food.
Occasionally, it may become necessary to prune or to replace a dead plant.
Diseased plants should be removed immediately.
Although confined plants tend to grow very slowly, any plant that has outgrown its environment should be replaced.