What Is a Substitute for Wood Ash & Charcoal in a Garden?

Soil Test

• Wood ash and charcoal don't work for all kinds of soil because they provide several nutrients and benefits. When soil has a low pH level but doesn't need potassium, for example, adding wood ash or charcoal can harm plants by putting too much potassium in the soil. Using a home soil test kit helps to determine soil's pH, potassium and organic matter levels. If your soil needs all three components, then wood ash and charcoal may be an inexpensive option, but they aren't your only option. If your soil needs only one or two components, it's best to use a substitute for the wood ash and charcoal to avoid creating inhospitable soil.

Potassium

• Potassium is one of the three main fertilizer ingredients. The other two main fertilizer ingredients are nitrogen and phosphorus. Adding a fertilizer high in potassium, such as a 2-2-10 fertilizer, can increase the soil's potassium level without using wood ash or charcoal. Other options include potash, which is a potassium compound for soil, or kelp, which is a 1-0-2 fertilizer.

Soil pH

• Soil pH is a measurement of the soil's acidity level. Most plants perform best in soil that has a pH range of 6.0 to 6.5, which is slightly acidic. A pH level of 7.0 is neutral. Adding wood ash or charcoal raises soil's pH level because each adds calcium, making the soil more alkaline. If your soil's pH measures lower than the desired numbers, then adding ground limestone can raise its pH level, just as wood ash and charcoal can. Because dolomitic limestone adds both calcium and magnesium, it works for soil that is low in magnesium and needs a higher pH level.

Soil Composition

• Many plants have specific soil drainage needs, performing best either in well-draining soil or soil that holds moisture. Adding wood ash and charcoal to soil makes it hold water better than it did previously. When soil is sandy or loamy, adding wood ash and charcoal to it can help keep soil moisture near plant roots longer than it would stay otherwise. Substituting compost or fallen tree leaves for wood ash or charcoal, however, also helps soil retain moisture but without the addition of extra calcium or potassium.