garden Q&A: consider ph before adding ashes
Q: I operate a woodstove during the heating months, producing buckets of ash from the hardwoods we burn (maple, oak, ash, cherry). Of what value are those ashes to my compost pile or to my garden directly? Is there any benefit to adding the ashes to my compost pile or directly to the garden and rototilling them into the soil in the spring? We have a number of flower beds around the yard. Are there any plants in particular that would benefit from having the ashes added to their beds?
A: Wood and leaf ash have been used by farmers and gardeners for hundreds of years 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 1.5 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 existing nutrient levels and soil pH. Because ashes are so alkaline, adding them to the soil raises the pH, making it less acidic. If the test results show a pH of 6.5 or higher, don't add those ashes. Doing so would raise the pH to nonoptimum 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 whack. 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 and make the soil so alkaline that most plants cannot thrive. I also would suggest you don't add ash to poorly drained soil because it reduces a soil's porosity.
If you do choose to add the 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.
Just in case you still haven't decided, I'm going to tell you what this “expert” does with our wood ashes — I compost them. Because I worry that I'll add too much or that I won't get them evenly spread, 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.
Send your gardening or landscaping questions to email@example.com or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.
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