When summer becomes nothing more than a memory, and the garden has gone to sleep for the winter, many gardeners revert to working inside. While caring for houseplants is somewhat satisfying, a potted plant sitting alone, on a table is just not the same as a garden filled with flowers.

A bottle garden (or terrarium) is a collection of compatible plants grown in an enclosed, or partially enclosed, clear container. This might be an interesting hobby for the dark evenings. Creating a terrarium filled with ferns and other small plants is a practical and fun way to have a miniature landscape inside your home. 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 large plastic water bottles. The choice is yours. 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. 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”.

LAYERS

Let us start by looking at the different layers you will need to make up the perfect growing medium for the plants to thrive in.

Layer 1. 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.

Layer 2. On top of the drainage layer, it is a good idea to spread a thin layer of activated charcoal (like you would use in an aquarium filter). This layer will help to clean the air of the fumes caused when the organic materials begin to decompose.

Layer 3. The third layer is a thin cover of sphagnum moss, spread 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.

Final layer. The final level is that of your soil. Many garden centres sell a potting mix specifically for terrariums and bottle gardens. 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 mould to each two parts of your usual mix. Never use beach sand in any potting mix as it has salt in it! Do not add any fertilizer to the potting mix. It already has enough nutrients to last a long time. Too much will cause the plants to out grow their surroundings, much too quickly.

If you intend to create a “desert garden” with cacti, be sure to add extra sand to the soil mixture, and additional gravel to the drainage level. The great thing about buying plants for terrariums and bottle gardens is that the plants will need to be as small as possible. This means that you will not have to pay a lot of money to stock your container. Most garden centres and DIY shops sell these plants for around €1 each so it is very affordable.

Although I have made a list here it concentrates more on how little or how much light the plants can tolerate you will probably have to experiment with the plants that are on offer in the shops. Try the carnivorous plants if you feel adventurous, they will be more expensive though. Most of the plants will outgrow their positions eventually so do not be afraid to move them around when necessary.

TYPES OF PLANTS SUITABLE (AND WIDELY AVAILABLE) FOR A BOTTLE GARDEN

Plants that need low light

Swedish Ivy

Birds nest Sansevaria

Maidenhair

spleenwort

Plants that need moderate light

Heart-leaved philodendron

Maidenhair fern

Miniature peperomia

Prayer plant

Spider plant

English ivy

Pitcher Plant

Plants that need bright light

Oxalis (shamrock)

Rosary vine

Venus fly trap

SETTING THE RIGHT SCENE

Your new landscape should be structured and set up for the best visual effect from the viewer’s 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, in much the same way that a hanging basket will be made up. 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.

PLANTING UP THE TERRARIUM

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 terrarium and 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.) The 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. (clear dishes, plastic sheeting, etc.)

Check it 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, 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 indeed needed, it should only be added a small amount at a time, since there is no place for the surplus water to run off. Generally, terrariums should not need fertilising, 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.

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