Small Piece of Charcoal Burning into Ash
(Image credit: Tomohiro Yamashita)

Is ash good for compost? Yes. Since ashes do not contain nitrogen and will not burn plants, they can be useful in the garden, especially in the compost pile. Wood ash compost can be a valuable source of lime, potassium, and other trace elements.

Fireplace Ashes for Compost

Composting ashes is an ideal way to put them to use in the garden. Fireplace ashes for compost can be used to help maintain the neutral condition of the compost. It can also add nutrients to the soil. Decomposing materials in the compost pile can become somewhat acidic, and wood ash can help offset this, as it's more alkaline in nature. However, it may not be a good idea to use charcoal ashes, such as those from grills. Compost with charcoal can have chemical residue from the additives in the charcoal. These chemicals can be harmful to plants, especially when used in large amounts. Therefore, it is better to stick with wood ash—provided that the wood used has not been treated or painted.

Using Wood Ash Compost Instead of Direct Ash Applications

Ashes tend to raise the soil pH, so you shouldn't use it directly on plants, especially acid-loving ones like rhododendrons, azaleas, and blueberries. Also, in high amounts, wood ash can inhibit plant growth by restricting nutrients, like iron. Don't apply it directly unless a soil test indicates a low pH level or low potassium. Adding wood ash within the compost pile, however, will lessen any chance of future issues and can be safely added to the soil as a balanced fertilizer. In addition to improving the soil health, adding wood ash compost around plants may be beneficial in repelling some types of insect pests, like slugs and snails. Composting ashes can add to the richness of your garden soil as well as being a convenient and eco-friendly way of disposing of your fireplace or campfire ashes.

Nikki Tilley
Senior Editor

Nikki Tilley has been gardening for nearly three decades. The former Senior Editor and Archivist of Gardening Know How, Nikki has also authored six gardening books.