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Knowledge to Grow by Karen Weiland - Wood Ash

So now that the weather is turning colder those wood stoves sure do feel good to warm our hands and feet at. The resulting wood ash can be used “judiciously” in the garden and landscape.

The main benefit from adding wood ash to the soil is the raising of its pH level, or to make it less acidic. Soil pH is a measure of acidity on a 14-point scale with 7 being neutral. Below 7 is acidic and above is alkaline. Slightly acidic is ideal for many plants as this is the range (5.5-7) in which most nutrients are available to them.

Generally wood ash contains trace amounts of micronutrients such as copper, zinc, manganese, iron and boron, less than 10 percent potash and 1 percent phosphate. Wood ash does not contain nitrogen and may contain some trace amounts of heavy metals like lead, nickel and chromium. A common liming material called calcium carbonate is the largest component of wood ash (about 25 to 45 percent).

Nutrients such as phosphorus, iron, potassium, zinc, copper, boron and manganese become chemically tied to the soil and thus less available for plant use when soil alkalinity increases and the pH rises above 7.0.

Wood ash, as you know, has a very fine particle size and will react quickly and completely when applied to the soil. For soils that can benefit from wood ash, a few guidelines need to be followed. Never use more than 20 pounds (roughly a five-gallon pail) per 1,000 sq. ft. Adding too much can do more harm than good, particularly since wood ashes can change the soil pH more quickly than most liming products. Apply ashes evenly and mix them into the soil. Do not leave lumps or piles on the surface of the soil. That would be like applying a large amount of lime to a small area. Rinse off any wood ash that comes into contact with nearby foliage. Never use wood ash around acid-loving plants like azaleas, rhododendrons and blueberries.

Soil composition varies from garden to garden and generally a small amount of wood ash can be added. It does help replenish some nutrients. If you don’t know your soils alkalinity or acidic level, have the soil tested.

As always, Happy Gardening!

The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange County.