For anyone who has ever owned a fireplace or wood burning stove, wood ash can seem like a messy byproduct. The ash seems to cling to everything and create a dirty mess in the home. But wood ash has many benign uses. The oldest recipes for soap involve wood ash and tallow. In the garden, wood ash can be worked into a compost pile if it is used carefully.
Wood ash has been used in the soil to improve its character since Roman times. These farmers, who didn't know why compost was so beneficial to soil, still dug trenches that they filled with manure, rotting hay, old leaves and wood ash to help improve their crops. According to soil scientist Dan Sullivan, of the Oregon State University Extension Service, farmers of the ancient world saw value in 'returning the ash to the soil.' By the 18th century, potash was such a popular amendment for soil in tree-deficient Europe, that North American trees were felled and burned to supply European soil with the product.
The ash from wood is the remains of a once-living tree. These ashes still contain many of the elements that the tree took from the soil as it grew. The elements include potassium, calcium and magnesium. When wood ash is added to compost, these elements become part of the finished product. In a compost pile, wood ash can help the pile maintain a pH neutral condition that is beneficial to the microbes that help to break down the organic material.
When collecting materials for a compost pile, each material you use is classified as either a green or brown. Green materials are rich in nitrogen. These materials are usually spongy or wet in nature, and may be prone to rotting as they decompose. Good examples include kitchen scraps or grass clippings. Brown material is rich in carbon. Newspaper would be classified as a brown material, as would dead leaves. Browns tend to be drier in nature, and can take a long time to decompose. Wood ash is considered to be an organic brown material.
Wood ash is a strong alkaline. It contains lye, which can be a caustic substance. When adding wood ash to a compost pile, it is a good idea to wear protective clothing, gloves and goggles. Since wood ash can be fine textured, it may also be a good idea to wear breathing protection to avoid contaminating your lungs with the ash.
Ash should be added sparingly to your compost pile as the pile is built up. The best method for building a compost pile is to alternate layers of greens and browns. Between each layer of compost, a fine dusting of wood ash should be applied.