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Description

A terrarium is a glass container, with or without a top, used for growing plants. Growing plants in glass containers has been done since early in the 19th Century. This fact sheet provides introductory information about how to plant and care for terrariums.

History

In 1829 surgeon, Dr. Nathaniel Ward, while studying the hatching of the adult sphinx moth, placed the cocoon in moist earth inside a sealed bottle and was surprised that grass and a tiny fern started to grow. He proceeded to develop large glass containers, known as "Wardian cases" and used these to ship plants, such as banana trees, tea plants, or young rubber trees, round the world. The cases were also used to exchange plants and stock botanical gardens with many new specimens. Dr. Ward's discovery also led to the Victorian craze for home versions of the Wardian case, early versions of today's terrariums.

Advantages of Using Terrariums

• Plants require almost no maintenance
• Ideal environment for plants that require constant moist soil and or atmosphere
• Plants grow slowly and evenly
• An interesting alternative to using pots when space is limited
• Easily moveable
• Good for miniature specialty gardens
• Safe around children and pets
• Fun to make

How Terrariums Work

Water evaporates in the warmth of the day, rises, cools and condenses as droplets of moisture on the sides of the container, eventually falling back to the earth and plants. Slight misting on the sides of the terrarium indicates a properly balanced terrarium.

Preferred Containers

• Clear glass is recommended so that maximum light can reach the plants.
• Plexiglas, lucite or other manmade plastics are not recommended because the water does not run down the sides of the container. Watering results in fog and the humidity can create warping that can cause seams to split.
• Any glass jar/large bottle can be recycled providing there is a neck opening of at least 6 cm.
• Must be the correct size for the chosen plants and allow room for growth
• If a top is needed, a glazier can cut glass to fit - usually 1/8 to 3/16 inches thick
• Terrariums do not require drain holes so, unlike other planting containers, holes are not necessary at the bottom of the container

Soil mixes/Additives

• Use clean, sterilized peat moss based soilless mix with vermiculite or perlite to enable the soil to hold moisture and oxygen or:
• Build your own soil mix: 3 parts sterilized potting soil; 2 parts perlite or sand; 1 part peat moss or vermiculite
• There should be an initial layer of gravel for drainage (one part gravel to two parts soilless mix)
• Add charcoal to absorb odours (one tablespoon per cup of drainage). In a small terrarium, omit the gravel and use charcoal
• Soil separator can be used to keep the layer of drainage/charcoal apart from the soilless mix. Use fibreglass drapery fabric, nylon tights, sheer drapery, screening (not metal) or landscape fabric
• Use sand in a desert terrarium. Sand should be bagged, washed and free of salts
• Leaf mold can be used for woodland soil mixes but should be sterilized
• Limestone can be used, especially for desert terrariums
• Bonemeal can be used in desert terrariums
• Do not use fertilizer in the initial planting

Plants

• Make sure the plants are insect and disease free because a terrarium is an ideal environment for their growth.
• Choose compact, bushy plants.
• Choose a variety of plants with an eye to shape, maximum height and spread, growing habit, texture and colour.
• Choose plants that can tolerate high humidity if in a closed container.

Tropical Terrariums

• Baby's tears Helxine soleirolii - moderate light
• Syngonium - low light
• Creeping fig Ficus repens - moderate light
• Bloodleaf Iresine lindenii
• Nerve plant Fittonia
• English Ivy Hedera Helix
• Pilea varieties: 'Moon Valley'
• Creeping Jenny Lysimachia nummularia 'Aurea'
• Aluminium plant Pilea cadieri
• Artillery fern Pilea microphylla
• Strawberry begonia
• Parlour palm Neanthe Bella - tolerant of low light
• Prayer plant Maranta - tolerant of most conditions except high light
• Podocarpus

Woodland Terrariums

• Norfolk Island Pine Araucaria - look for small bonsai
• Partridgeberry Mirchella repens
• Ferns: Asparagus fern Asparagus plumosa - not a true fern
• Fluffy ruffles Nephrolepis exaltata
• Rabbitsfoot Davallia
• Maidenhair Adantium pedatum
• Table fern Pteris
• Club Moss Lycopodium
• Selaginella
• Holly fern Cyrtomiun

Desert Terrariums

Choose succulents and cacti from arid and semi arid regions

Making a Desert Terrarium

Make effective use of different tones/colours of earth and sand:

• Dark brown - potting soil
• Medium brown - cactus soil
• Yellow - sand

Method

1. Cut stiff paper to the height of your container - 1 to 2 inch smaller than the walls.
2. Tape the ends to make a dam.
3. Place soil mix inside the dam while adding layers of colour outside the dam until 2 cm from the top. Make the levels the same height.
4. Remove the dam slowly and add soil mix on top.
5. Add rocks, pebbles, dead branches and random groupings of succulents.
6. Add gravel or sand to the top.
7. When watering do not drench but use a watering can with a fine spray.
8. Fertilize lightly in the growing season: half strength every 6 to 8 weeks.

Bottle Gardens

• The dry, clean bottle must have a diameter of at least 5 to 8 cm - check diameter by making a circle with thumb and forefinger.
• Allow room for growth, as there is no room for pruning.
• Use 4 cm of drainage material; 1.5 cm of charcoal; a soil separator; 6 cups of soil to 1 gallon of container.
• Use a stick to open the planting holes and tongs to position plants
• Use tongs for positioning rocks, pebbles or tiny sculptures
• Tamp earth gently after planting using a stick with a cork or stiff sponge at the end.
• Water the plants 24 hours before planting.

Carnivorous Plant Terrariums

• Use an acid-based medium.
• Plants should be planted loosely in sphagnum moss.
• Place near bright light.
• Temperature should be 65 to 75 degrees, 10 degrees less at night.
• Do not fertilize.
• Add ants, flies, crickets - live or dead.
• The terrarium lid can be removed during the hot humid summer months.

Maintaining a Terrarium

1. Moisture balance:
• After planting an 'open' terrarium mist plants to clean them and to clean the glass walls of the container.
• If using a 'closed' terrarium keep the lid off until the plant foliage dries.
• The water in the bottom should not be more than _ inch deep in a terrarium after planting.
• Once the moisture cycle is established, it is self-perpetuating.
• Changes in light and heat are not likely to cause problems in the long run.
• If moisture does not appear on the glass for over a week, add some water.
• Most terrariums (if closed) need added water every 3 or 4 months. Remember that the length of time will vary with the particular growing environment.
• Open terrariums require moisture more frequently but not as frequently as plants in pots
2. Plant growth:
• Pinch back regularly to promote bushy growth.
• Prune woody growth to encourage compact growth.
• Always cut back to leaf or branch joint.
• Remove plants if the terrarium looks overgrown or if diseased or infested with insects.
3. Temperature:
• Maintain daytime temperature range of 65 - 80 degrees with a night-time temperature of ten degrees lower.
• A sealed terrarium is protected against sudden temperature changes, drafts or excessive dryness, as long as the environmental change does not last longer than 48 hours.
4. Light
• If light conditions are not ideal, the plants will stretch or look too pale.
• Direct light is required for desert terrariums with no lid.
• Indirect strong light (east or west facing window) is excellent for tropical or woodland terrariums or up to 1.5 m away from a south facing window.
• Medium light is acceptable for woodland or tropical terrariums (1.5 to 4 m away from south, east or west facing windows).
• Low light is used for low light tropicals (4 to 6 m away from sunny windows and 1.5 to 3 m away from north, east or west windows).
5. Fertilizing
• Use a seaweed based fertilizer or fish emulsion, 1 to 4 strength, in spring to the middle of summer.
• Alternatively, use water-soluble fertilizer at 1/10 of normal strength.
• Plant Replacement
• If plants become badly infected or die, clear everything out, sterilize and begin again
• Open terrariums are less subject to disease

Resources

The Toronto Botanical Garden Weston Family Library is an excellent source for horticultural information.

Books

• Kayatta, Ken and S. Schmidt. Successful Terrariums - A Step by Step Guide. N.Y. New York: Houghton Mifflin Company, 1975
• Ashberry, Anne. Bottle Gardens and Fern Cases. N.Y. New York: Bonanza Books, 1964

Factsheets are produced by the Toronto Master Gardeners in association with the Toronto Botanical Garden. They provide introductory information about a broad range of horticultural topics and are intended for personal use and study purposes. Should your gardening group or organization wish to use multiple copies we ask that you inform the Toronto Botanical Garden at info@torontobotanicalgarden.ca.

Date revised: November 18, 2007