Bell Jars for Terrarium Plants

Material

• Glass bell jars are the most common kind available because they provide the best clarity and temperature control. Very thick glass that is hard to see through should be avoided because it prevents light from reaching the plant inside each bell jar. Antique or vintage bell jars can be attractive, although their glass may have chips or air bubbles. Most of those imperfections do not affect plants, but avoid bell jars with cracks or chips large enough to cause light to refract away from the jars.

Transparency

• Bell jars used as terrariums need to be clear so light can get to the plants. A slight tint to the glass may allow enough light through it for plants that need shade. Heavily tinted or fully colored glass does not allow enough light through it for plants to survive. Also, colored glass changes the light spectrum that reaches plants, and so it can prevent photosynthesis. Green glass is especially problematic for plants and should be avoided.

Size

• Plants create their own air, which is why they can survive in closed containers such as bell jars. Each jar must be large enough to allow air to circulate or the plant could suffocate. Every jar's interior also must include enough room for the plant to grow. The top of a plant should reach only one-half of its bell jar's height in order to allow growing space and air circulation. If, however, a bell jar is twice as wide as the container the plant is in, then the headroom requirement can be reduced to one-third of the jar's height because that jar offers more air circulation room around the plant.

Plants

• Choosing the right plant for a bell jar is important. The jar's closed environment increases humidity inside the jar. Desert plants and plants that need dry soil and low humidity, such as cacti and other succulents, should not be grown under a bell jar because the humidity will cause them to break down and begin to decompose. Plants such as ivy, ferns and tropical plants are ideal for growing under bell jars.