January 3, 2013
To avoid making your garden-bed soil overly alkaline, dump wood ash left over from your winter fires into your compost bin. Photo by Jessica Walliser (HobbyFarms.com)
Photo by Jessica Walliser
To avoid making your garden-bed soil overly alkaline, dump wood ash left over from your winter fires into your compost bin.

Happy New Year everyone! I wish you all a successful and productive 2013.

We’ve been busy trying to stay warm here in western Pennsylvania and have been enjoying many fires in our fireplace. As a result, we have a lot of wood ash. I’m often asked by gardeners if it is safe to use fireplace ashes in the garden. I thought you might like the low-down on this, as well.

Both wood and leaf ash has been used for centuries by gardeners to amend their soil. This, however, doesn’t mean that it’s always a good practice. We’ve learned a lot about soil and plant health over the years, and as a result, the decision to use ashes in the garden has become a hot topic in the gardening world. I’ll give you some facts, then you can decide for yourself if it’s something you want to do.

First, one of the reasons folks use ash in their gardens is its nutritional content. Ash contains about 1½ percent phosphorus and 7 percent potassium, two essential nutrients for plant growth. If your soil has a deficiency in potassium, adding a few ashes would help boost the levels. But, to make an informed decision, you should first take a soil test in the garden to determine both existing nutrient levels and soil pH. (You can do this by sending a soil sample to a lab at your local cooperative extension.) Because ashes are so alkaline, adding them to the soil also raises the pH, making it less acidic. If the test results show a pH of 6.5 or higher, don’t add the ashes. Doing so would raise the pH to non-optimum levels.

In western Pennsylvania we tend to have slightly acidic soils, so adding a tiny bit of ash to the garden each year usually doesn’t throw the pH too out of wack. That being said, the reason some experts are no longer recommending the usage of ash in the garden is because a little goes a long way and putting even a little too much on the soil can wreak havoc on soil organisms, making the soil so alkaline that most plants cannot thrive. I would also suggest you don’t add ash to poorly drained soil because it reduces a soil’s porosity. 

If you do choose to add wood ash to your garden, be sure to spread it evenly and in minimal amounts. Come spring, mix it thoroughly into the soil to avoid patches of overly alkaline soil.

Because I prefer to avoid the possibility of over-doing it, instead of adding our ashes directly to the garden, here’s what I do with them (and you can confirm this with my husband who got admonished last week for dumping a pile of wood ashes into a bed of evergreens): I compost them. I worry that I’ll add too much to the garden beds or that I won’t get them evenly spread, so I cut the risk by adding the ashes to my big compost pile. They get dumped on top or saved in a metal bucket to be blended into the pile during the growing season. The mixture of organic matter that goes into my pile helps neutralize the ash’s pH, and by the time the compost is fully cooked, the pH is not a concern. Obviously you don’t want to add excessive amounts of ash to a small compost bin, but larger piles can handle quite a bit. 

For more on what you can add to your compost pile, download and print this guide compostable green and brown materials. 

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