Wood ashes can be used for composting

By Theresa Semchee

Ohio certified volunteer naturalist

This is the time of the year that we all like to sit around a campfire or light the fireplace on a chilly night. And after a few fires, our ashes start to accumulate and it’s time to scoop them out.

Do those ashes have a purpose? Yes they do.

Throughout my research, I found some very interesting uses for the ashes, but today I want to tell you about composting them. Wood ashes can be a great addition to compost piles and/or your garden.

When I use the term wood ash, I am referring to the entire remnants of a wood-burning fire. In reality, what remains after a typical fire is both ash and charcoal. Ash is the fine grey substance, whereas charcoal describes the black chunks of material that accompany the ash. Both ash and charcoal can offer tremendous benefits to your compost pile and garden.

Should I put wood ash in my garden? This was my question to the extension office a couple of years ago. I did some research and thought there are probably others who are wondering the same thing.

The short answer is yes. That being said, you need to be careful how and where you use it.

Wood-ash fertilizer is best used either lightly scattered or by first being composted along with the rest of your compost. This is because wood ash will produce lye and salts if it gets wet. In small quantities, the lye and salt will not cause problems, but in large amounts it will burn your plants. It will increase your pH just as if you were adding lime, but only by about half as much. If composted first, the lye and salts will leach away.

During the composting process, these nutrients will be shuttled through, and tied up in, the bodies of your compost microbes. Once your compost is applied to your garden, these nutrients will gradually make their way into your plants via plant-microbe exchanges. By composting wood ash you also will be adding the following micro-nutrients back into your pile – potassium, lime, iron, magnesium, boron, copper and zinc.

Not all wood–ash fertilizers are the same. If you burn hardwoods, such as oak and maple, the nutrients and minerals in the ash will be much higher. If you are burning mostly softwoods, such as pine and firs, there will be less nutrients and minerals in your ash.

Whether you are composting wood ash or using it directly on your garden, it tends to increase pH levels. Wood ashes are 25 percent calcium carbonate, which makes them quite alkaline (pH greater than 7.0) by nature. Calcium is a very critical nutrient in composting and gardening success. If your soil is quite acidic, the addition of wood ash is very beneficial. However, if your soil is already alkaline, using a large amount of wood ash can be detrimental. Do not use wood ashes to fertilize acid-loving plants (azaleas, gardenias, and blueberries).

Soil testing is always recommended. For details on soil testing in Mahoning County, visit go.osu.edu/soiltesting. For more information on using ashes, visit http://go.osu.edu/useashes.