Can you compost ashes?


A reader writes in with a question about whether it is safe to compost ashes.

Can ashes from a fireplace be used in a compost pile? Would it be considered “brown” stuff rather than “green” stuff, The only things in the ashes would be newspaper, pine and other dried natural wood; nothing chemically treated.

The sort answer is yes, you can compost wood ashes, in limited quantities.

You don’t want to overwhelm your compost pile with too much of any single ingredient, whether it is ashes or anything else.

Ashes from coal or barbecue briquettes should NOT be composted, because they can contain chemicals that might harm your soil. (Although I must point out that there was a study by Washington State University that determined coal ash up to a certain percentage in compost didn’t harm anything. So maybe I’m just being overly cautious.)

I personally do not like composting wood ashes though, because ashes change the pH of the soil. Ashes are very alkaline.

In fact, if you live in a dry, desert area that already has poor, alkaline soil, you should avoid even wood ash.

Oregon State University Extension Agency has a very thorough article about wood ash and gardening and composting, that is mostly positive about using wood ash with gardening and with composting.

They also mention the pH issue.

For the home gardener, however, wood ash can be a valuable source of lime, potassium and trace elements.

“Since wood ash is derived from plant material, it contains most of the 13 essential nutrients the soil must supply for plant growth,” said Sullivan. “When wood burns, nitrogen and sulfur are lost as gases, and calcium, potassium, magnesium and trace element compounds remain. The carbonates and oxides remaining after wood burning are valuable liming agents, raising pH, thereby helping to neutralize acid soils.”

Where soils are acid and low in potassium, wood ash is beneficial to most garden plants except acid-loving plants such as blueberries, rhododendrons and azaleas. Use wood ash on flower beds, lawns and shrubs.

Hope this is helpful!

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