Ash Wednesday for Gardeners
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By Will Summers, Washington County Master Gardener/Master Naturalist
Wood ashes are the essential elements left over after the combustion of organic material, primarily wood. Wood ashes are gray and powdery. Black ashes indicate incomplete combustion leaving remnants of unburned carbon or “charcoal” which are typically black. The source of my wood ash is our wood burning stove, but others may be found in fireplaces, outdoor fire pits and even some furnaces. These ashes represent the remaining elements of living plants, primarily trees. Wood ash, if handled correctly, represents opportunities to replenish nutritional plant elements lost in the soil.
Please be aware of the source of your wood ash. Ash from preservative-treated wood, painted wood, trash or plastics should never be used in your garden. Ashes from oak, hickory and other hardwoods contain more valuable nutrients than that of pine, poplar, cottonwood or other softwoods. Be careful about using wood taken from pallets that may have been preservative treated or had dangerous chemicals spilled on them.
Wood ash is the best source of potassium, previously called “Pot-ash” by our ancestors. Potassium is one of the main ingredients of the “Big-Three” nutrients: “N-P-K”—nitrogen, phosphorus and potassium. (K is the chemical symbol for potassium.) It also contains an important source of calcium carbonate, commonly associated as “lime”. However, wood ash is the source of many other valuable soil micro-nutrients such as sulfur, magnesium, copper and others.
Added benefits from wood ash is to buffer soil ph. Heavily used, composted, or fertilized soils in our area gradually become lower pH, or acidic. Acid soils frequently reduce plant growth or make them susceptible to disease and pest problems. Gardeners use lime to buffer acidic soil. Wood ash contains approximately half the soil buffering potential as commercial, finely ground lime.
Wood ashes must be kept dry and out of weather until ready to use to preserve their potency. Wood ash may be added dry and directly to your garden in many ways. I prefer spreading light dust over the top of recently cultivated beds. Please avoid creating a dense clump of ashes, which may be too harsh and burn young plants. Ashes may also be added into your compost pile and well-mixed, before applying into your garden. Lastly, mix one cup of dry wood ashes per gallon of water to make a liquid fertilizer. Water plants once with ash-water to young plants to improve root growth in early summer. Apply your leftover wood ashes generously to your lawn grass areas, as you would commercially ground lime.
Wood ashes were once used to make lye-soap. Wood ashes produce lye, a caustic material. Wood ashes are extremely dusty, and gardeners should avoid breathing the fine particles. Also, avoid direct contact with the skin for extended periods and wear gloves if possible. Children should be always kept from wood ash.
Wood ash benefits many garden plants and vegetables, especially asparagus, garlic, onions and tomatoes. However, do not apply wood ash materials on or near any acid-loving plants such as azaleas, rhododendrons, hollies, red maple, birch, pin oak, and especially blueberries and potatoes. Consider using a pH meter to monitor your soil acidity or alkalinity.
We hope you will continue or are able to distribute valuable plant nutrients back into your property for healthier plants. Please direct any gardening questions to your local University of Illinois Master Gardeners or your local U of I Extension office. Please join us at the Midwest Herb and Garden Show on March 6 and 7 at the Times Square Mall in Mt Vernon, Illinois.