Applying wood ash to the garden three to four weeks before planting increases potassium and phosphorus levels in the soil, which strengthens root systems.
Wood ash was commonly used as fertiliser in centuries past because it contains phosphorus and potassium, two essential nutrients that promote healthy root growth in plants. Ordinary wood ash from fireplaces or stoves can be spread directly on the soil in the spring or can be composted with leaves and vegetable matter.
The best time to spread ash on the lawn or garden is three to four weeks before planting, or in the very early spring. Five to 4.54 Kilogram per 100 square feet is the standard application.
Wood ash can also be added to a compost pile but only in very small amounts. The proper ratio of wood ash to plant matter in a mulch pile is 400:1.
Using too much wood ash in compost in a garden or spreading it too heavily in its raw state directly onto a lawn can cause salt to build up in the soil. Salty soil will kill most plants, so when using wood ash, proper proportions and ratios should be carefully observed.
Potassium and phosphorus are essential compounds in most garden fertilisers and are present in wood ash in useful amounts. Wood ash with potassium and phosphorus promotes root growth. Strong roots systems protect plants from stress and disease.