Do Open-Top Plant Terrariums Need Horticultural Charcoal?

Odor

• One of the main reasons for adding horticultural charcoal to a terrarium is to reduce odors. An open terrarium has more air flow, which reduces the chances that you'll have mold, fungus and other conditions that lead to stale odors. If your terrarium is wide and shallow, you can get away with leaving out the charcoal. If your terrarium has tall sides or a small opening, you'll have less air flow. In this case, charcoal would help make sure your terrarium doesn't develop unpleasant odors.

Toxins

• Charchol also helps remove toxins from water. In a traditional closed terrarium, water treatment chemicals that dissipate into the air don't have a chance to escape. Some terrarium plants are sensitive to the chemicals in tap water and can show signs of damage or ill health. Charcoal helps absorb these chemicals from the water, along with any other toxins that might be in the air and soil. Again, the larger the opening, the lower the sides and the more airflow you have in your terrarium, the less you'll need charcoal.

Decoration

• Some people like to add charcoal simply because it adds a decorative element, or the look of multiple layers to the terrarium. If you don't need charcoal in your terrarium and you still want this layered look, you can achieve it by adding several layers of rocks, aquarium gravel, beads, marbles or other decorative elements to your terrarium. Place the decorative materials at the bottom of the terrarium. Cover them with a 1-inch layer of sheet moss or sphagnum moss, then add your soil and plants.

Types of Charcoal

• You may have a hard time finding charcoal. The charcoal you need isn't the type you use in your grill. What you should buy is horticultural charcoal. It looks more like aquarium gravel than the chunky briquettes. It's usually near the pumice and other soil additives in garden centers. If you can't find horticultural charcoal at a garden center, you can use the charcoal sold by pet stores for aquarium filtration systems. As a last resort, you can purchase aquarium filter pads that contain charcoal and break them open.