[header] How to use ashes as fertilizer [title] Use wood ashes as a soil amendment in the early spring while the soil is dry and before the plant life has begun to actively grow. [substeps] Nearly all plants benefit from the potash content of wood ashes. Other components of the ashes are beneficial to the soil and plant growth as well. 
Because the wood ashes act as a liming agent, they reduce the acidity of the soil. Plants that prefer acidic soil such as blueberries, azaleas or rhododendrons will not thrive if wood ashes are applied.