How to Make a Cool Temperature Terrarium

A terrarium is a tiny ecosystem.

A terrarium is an individual environment where plants, moisture and light create a working representation of an ecosystem. A cool temperature terrarium mimics a woodland setting by using filtered light, low growing ferns and lichen and a semi-moist, controlled climate, conducive to plant survival. With the correct supplies and plants, you can create a cool temperature terrarium that will thrive for years with very little attention.

Things You'll Need

• Glass terrarium (or bowl)
• Small rocks
• Sterilized potting soil
• Peat moss
• Vermiculite
• Activated charcoal
• Plants
• Fluorescent light source
• Hygrometer
• Location with temperature between 40 and 65 degrees F

Instructions

Prepare the Terrarium

1. Choose a glass terrarium to suit your design needs. A fish aquarium works well, as does a large glass fish bowl with a cover. Size is the more important factor since it will determine how many plants are included in your terrarium. Keep in mind that it is harder to clean a plastic terrarium as it tends to cloud with age.

2. Ensure that you have an adequately cool location before making the terrarium. In northern areas, a basement is a good choice but if the temperature rises above 65 degrees F for longer than a day or two, your plants may suffer.

3. Prepare the medium in which your plants will grow. It is imperative that you only use sterilized potting soil, peat moss and vermiculite because bacteria or fungus, present in garden soil, can destroy your plants.

4. Sterilize the small rocks by placing them in a large pan of water and bringing the water to a boil. Allow the water to cool and drain the rocks.

5. Layer 2 inches of rocks on the bottom of your terrarium, followed by a ½-inch layer of activated charcoal, covered by at least 3 inches of peat moss and potting soil combined in equal amounts. Your substrate will measure approximately 4 to 5 inches in depth.

Plant and Maintain the Terrarium

1. Select your plants based upon the ability to survive in cool temperatures. In addition, plants that maintain a low growth pattern are desirable since the terrarium offers a limited growing space. Some good choices include the Venus fly trap, watercress, sweet flag, woodland moss, water clover and the cobra plant. Some varieties of ivy are suitable as long as they do not need ventilation.

2. Arrange your plants in an attractive pattern. If your terrarium has only one viewable angle, place the taller plants in the back and smaller ones in the front. If the terrarium is round, place the tallest specimens in the middle and surround them with low growing plants.

3. Add water sparingly. A common mistake of new terrarium owners is to add water as you would to an open air plant. Since a cool temperature terrarium is a sealed ecosystem, a little bit of water goes a long way. The general rule is to provide ½ cup of water for every square foot of terrarium planting surface. Use distilled or bottled water.

4. 

   Place a hygrometer outside your terrarium with leads that run inside and adhere to the terrarium’s inner surface. With a hygrometer, you can monitor the interior temperature.

5. Cover your finished terrarium and place it in a cool area, out of direct sunlight. Remember that even if the location is cool, sunshine on the terrarium will raise the temperature inside quickly. Instead, opt for a northern window or supply a fluorescent light above the terrarium.

Tips & Warnings

• Add only a tiny bit of fertilizer, if desired, once a year.

• Do not use incandescent lights near your terrarium as they put off heat and may raise the temperature inside.