Wood ash from fireplaces can improve soil
For gardeners who heat their homes in winter using stoves or fireplaces, good-quality wood ashes can be a soilamendment bonus. But if applied improperly, they can be a caustic topping for foliage-heavy plants and seedlings.
The primary benefits of recycling wood ash into the soil are for fertilizing and raising pH levels to make soil less acidic, said Leonard Perry, horticulture professor emeritus with the University of Vermont.
Soil pH acidity is measured on a 14point scale, with 7 being neutral. Anything below 7 is classified acidic. Anything above that is alkaline.
Always test the soil before spreading ashes.
“Too high a pH will bind up micronutrients that your crops need,” said Julia Gaskin, a land application specialist with the University of Georgia Extension Service. “If you are just getting started in a garden spot, soil-test every year until you get the fertility and soil organic matter right. Then you can test every other year or so.”
Wood ash contains calcium, magnesium, and potassium among a dozen or more important nutrients. “They vary widely with the types of trees being burned,” Gaskin said.
Avoid using fireplace or wood ashes from pressure-treated wood, painted wood and cardboard. They carry chemicals that can harm plants. The same goes for charcoal residue from BBQ grills, fake fireplace logs and coal. Those should go to the landfill.
Lawns needing lime and potassium benefit from wood ash – 10 to 15 pounds per 1,000 square feet, Perry said. “This is the amount you may get from one cord of firewood,” he said.
Spreading wood ash on compost piles keeps the acidity level near neutral. “Sprinkle some on each layer of compost as you build the pile,” Perry said. “Another option is to store wood ashes dry, then make a ‘tea’ with them during the growing season for watering plants and so providing some nutrition.”
Do not spread ashes around acid-loving plants like blueberries, strawberries, azaleas, rhododendrons, camellias, holly, potatoes or parsley. Plants that thrive with a dressing of wood ash include garlic, chives, leeks, lettuces, asparagus and stone-fruit trees.