How to Use Wood Ash
On lawn and garden; never in the compost pile
If you’re burning wood, you get ashes. A reader asked if he could dump his ashes in the compost pile. My answer was a resounding no.
Wood ashes are basic in nature and contain high levels of oxides, making them very reactive in raising the pH. Composting systems perform at their best when the feedstocks — those materials that are undergoing decomposition — are slightly acid. So adding wood ashes to an active composting pile will delay and/or stop the composting process.
Store wood ashes in covered metal containers and keep them dry. They should never be stored in an open container where they can absorb water. I can remember watching my grandmother pour dishwater over a bed of wood ashes to extract a lye solution she used to make lye-soap. (Remember the song “Grandma’s Lye Soap”?) I can also remember the strainer she used becoming very hot after the lye water had drained away.
Wood ashes are best applied directly on the garden or on the lawn. Ashes must be cool and dry when they are applied. Ashes spread in a garden and covered with dry leaves can start fires. I know because I’ve seen it happen.
When applying ashes on lawns with a fertilizer spreader, first screen them through a half-inch screen to remove pieces of charred or raw wood. Directly from the container, they should be spread as uniformly as possible; use a lawn rake to spread them around to avoid creating hot spots that can kill the roots of the grass. Spread the ashes on a calm day, avoid inhaling the dust and wear safety goggles to avoid eye contact.
In general, I recommend spreading a five-gallon pail of wood ashes over 100 to 200 square feet, especially on lawns. Higher levels can be applied on garden soils that are to be rototilled.
Wood ashes are a tremendous source of calcium, potassium and some phosphorus as well as essential trace elements. If you are using wood ashes to maintain the pH of your lawn or garden, have your soil tested to avoid excessive high soil pHs and to assure that your soils contain adequate amounts of magnesium (Mg). Wood ashes tend to be almost free of magnesium, which is essential for the manufacturing of chlorophyll in plants.
Save some of your wood ashes to spread around the zucchini plants this summer to help in controlling the stem borer. Before the zucchini plant starts spreading, apply a thin layer about two-feet wide around each plant. It will not provide 100 percent protection, but it does reduce infections.