Feed wood ashes to your garden

Feed wood ashes to your garden

Many Rogue Valley homes, especially in the rural areas, are heated with wood. Aged madrone and oak are favorites. Native to the area, each burns warm and long, helping to keep overnight household temperatures comfortable.

Once a log has burned, what's left is ash, a valuable byproduct that can be used as garden fertilizer.

Wood ashes have long been used as plant food. When the human species was discovering plant cultivation, someone noticed wood ashes made a slurry with water that seeped from a cooking pot. This mix — not surprisingly called "pot ash" — can be spread around plants as a fertilizer.

Wood ashes contain a high amount of the nutrient potassium, essential for healthy plant growth.

Wood ashes are best turned into the garden soil in spring. Saving wood ashes through the winter, storing and protecting them from the rain helps to retain their nutrients, which are converted to plant food when mixed into the soil. Metal garbage cans are ideal storage containers for wood ashes. The cover protects them, keeps rain out and, most importantly, the metal container is fireproof. Winter house fires easily can be set by the improper transfer of hot ashes from wood stoves or fireplaces.

The fertilizer value of wood ashes is 0-2-7: no nitrogen but fairly high in potassium (7 percent) while containing 2 percent phosphorus. In addition, wood ashes also contain 5 percent magnesium, another vital plant nutrient.

The fertilizer value differs depending on the type of wood. Ash from hardwoods, such as oak, may contain up to 10 percent potassium while the ash from softwood conifers (Douglas fir/pine) contain only 2 percent.

In addition, wood ashes are a good source of calcium, containing 60 percent of the liming capability of dolomite or limestone. Applying it at a rate of 3 pounds per 100 square feet helps to raise the pH of the soil, encouraging the performance of crops that prefer a more neutral soil.

Vegetable crops that can benefit from such an application include the cabbage family, onions, beans, corn and a variety of root crops. Avoid using wood ashes on acid-loving crops such as tomatoes, peppers, strawberries and most vine berries, as they prefer acidic soil with a pH in the 6.0 range.

Most fruit trees could benefit from a sprinkling of wood ashes applied on the soil surface over the drip line (the circle directly beneath the outer branches). Apply this top dressing through the fall and winter and let rains leach the nutrients to the surface roots.

Most garden soils could benefit from an application of 3 pounds of wood ashes per 100 square feet. Avoid turning under wood ashes with manure at the same time. This combination encourages the production of ammonia, which literally vaporizes the nitrogen from the manure into the atmosphere. Wait three or more days between applying wood ashes and manure.

So save up those ashes if you heat with wood. It's free and organic — and it'll help you eat better.

David James has been writing gardening stories in Southern Oregon for 35 years. Contact him at djames@oigp.net.

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