What Is Activated Charcoal: Can Charcoal Be Composted For Odor Control

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By Mary H. Dyer, Master Naturalist and Master Gardener

What is activated charcoal? Used in many commercial, industrial and household applications, activated charcoal is charcoal that has been treated with oxygen, which creates a fine, porous material. The millions of tiny pores work like a sponge that can absorb certain toxins. Using activated charcoal in compost and garden soil is an effective way to neutralize certain chemicals, as the substance can absorb up to 200 times its own weight. It may also help staunch unpleasant aromas, including smelly compost.

Can Charcoal Be Composted?

Many commercial compost bins and buckets come with an activated charcoal filter in the lid, which helps to neutralize odors. As a general rule, activated and horticultural charcoal can safely be incorporated into compost, and small amounts will help to neutralize unpleasant odors.

However, charcoal from barbecue briquettes or your fireplace charcoal ashes in compost should be used sparingly, as too much can raise the pH level of the compost beyond the desired level of 6.8 to 7.0.

Using Activated Charcoal in Compost

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In general, you should limit your use of activated charcoal to about a cup of charcoal for each square foot of compost. One caveat: if you use commercial briquettes, read the label and don’t add briquettes to your garden if the product contains lighter fluid or other chemicals that make briquettes easier to light.

Horticultural Charcoal vs. Activated Charcoal

Horticultural charcoal has many positive qualities but, unlike activated charcoal, horticultural charcoal doesn’t have spongy air pockets, so it lacks the ability to absorb odors or toxins. However, horticultural charcoal is a lightweight material that may improve poor soil by improving drainage and increasing the soil’s moisture-retaining capabilities. It may also reduce leaching of nutrients from the soil. Use horticultural charcoal in small quantities – no more than one part charcoal to nine parts soil or potting mix.

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