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How to Build a Terrarium

A terrarium is a container made of glass or other clear material, enclosing a garden of small plants. Terrariums are usually sealed, and therefore need little or no care. They water themselves. The containers don't have to be specifically designed as terrariums. You could try a large glass cookie jar, a fish tank with a lid, decorative bowls with lids, or wine casks, water bottles or old olive oil bottles. Stand it up or lay it on its side. You are limited only by your imagination and the plants you want to put in it.

Terrariums were very popular back in the '70s, but fell out of favour for a few years... well, maybe 30 years. But they are making a comeback, now. They're also an interesting project for children.

How Does it Work?

All plants breathe, taking in carbon dioxide and giving off oxygen. It takes in sunlight and carbon dioxide and through photosynthesis, produces food for itself and gives off the oxygen. It's an old recycle plant.

Once you've planted a terrarium, and watered it, you seal it up. After that, as the moisture in the soil condenses it will turn back into moisture and run down the sides, effectively watering the plants. You can have a terrarium that is not sealed, but it will need you to provide some watering, because the moisture can escape throught the top.

What Kind of Plants Will Work?

There are lots of dwarf plants available, and these usually will do fine. You can also purchase small, inexpensive baby plants from many garden centres. Make sure they do not need to be kept in a dry environment, however, as your terrarium will not meet that criteria. The environment is not ideal for most regular-sized plants, but many normal houseplants do well in terrariums and will just grow quite slowly.

My Tools Don't Fit!

You will have to find or modify tools to fit through the neck of your container. With a fish tank, tools are not a problem, and that's one reason many people start with one. If you're not keen on the fish tank idea, however, or want a narrow-neck terrarium, you still need to dig holes, place plants, tamp plants in place and add water. There are fancy tool sets available if you have the funds, other wise you'll have to make some up. One handy tool is a grabbing tool, formerly used to snag fallen screws from the inside of a computer. A funnel will be necessary to direct the soil to where you want it. The funnel can also be used in conjunction with a long, thin pipe, to direct water into the terrarium without creating a basin or washing out roots of a plant. Also consider the pipe and funnel combination to direct decorative sand placement, if that's what you like. Include chopsticks in your toolkit, especially if you can use them properly.


A container with a cork or lid
Tools with which to work
Ornamental or decorative elements (rocks, stones, twigs, etc.)
Distilled water

Why Distilled Water

Our tap water contains a lot of chemicals, like chlorine and flouride, and other things that you have likely heard about on the news. Using this water in a closed environment just intensifies things. If you can avoid it, why not err on the cautious side and do so.

How Many Plants?

For a small container, perhaps a one-half gallon jar or less, you should consider no more than one plant plus some ground cover and decorative elements. A container from one to five gallons in size could take 2 to 5 plants, and a large container will take even more. You will want to consider large you expect them to grow. Don't crowd. You can always add an additional plant or two, once you get going.

It is not recommended that you try fuzzy- or furry-leaved plants. Because they hold the moisture, they tend to rot in the closed environment.

How Much Soil and Charcoal?

You will need enough soil to cover the bottom of your terrarium to a depth that will cover the roots of the small plants you will purchase. A soil-less mix is best, with humus, sand, peat and vermiculite. Most potting soils are made up of a combination containing these. There should be enough charcoal to cover the bottom of the terrarium to a depth perhaps 1/4 of the soil depth. Its purpose is to stop the soil from molding and to provide drainage so that your plants' roots are not sat in water in the soil.

What Light, In Yonder Window Should Break?

Indirect light is what a terrarium most likes. It should never be placed in direct sun, however, or you will cook your plants in no time. Lots of light, behind sheers, would be fine.

Problems? What Problems?

- Until things settle down, and even then sometimes, you may get mold. Watch for it, and get it out as soon as you spot it.
- Initially, you may see too much moisture on the sides of the terrarium. Just take the top off and let some escape. Eventually, it will likely sort itself out. You don't mind seeing some condensation, but you should ideally be able to see the plants, as well.
- Plants getting too much, or too little water will not do well. Monitor the terrarium until it gets settled down, and make sure it's doing well. You may have to add more soil, or more water to get it going, or let it dry out a bit.

Vivarium Terrariums

When you've mastered the basics, you can think of new ways to make your terrarium concept more exciting, like adding an animal. A lizard is a good choice. The animal can breathe because, remember, the plants produce oxygen. Do some research to see what would make a home for your animal of choice.

Helen Kirkup is a Master Gardener and writer.

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