Fire pit ashes in garden soil

Asked April 25, 2020, 10:17 AM EDT

is it safe to use ashes from our firepit to amend soil in our garden?

Oakland County Michigan

1 Response


Using ash depends on what you burned in the firepit, the soil levels of potassium already present in your soil, and your soil pH. Ash can raise your soil pH, and if soil is already pH7.5 or higher adding ash is not recommended. . If you haven’t had a soil test in 3 years or more it is a good idea to test it-

Please see this response to another question on using ash as a soil amendment:

“Wood ash is a good source of potassium. You can use wood ash sparingly as a fertilizer or liming material on vegetable gardens, flower beds, lawns and most shrubs. Hardwood weighs more per cord than soft woods and yield more ash per pound of wood.

Apply wood ashes evenly, and if possible mix them into the soil. Never leave ashes on the surface in lumps or piles. If ashes are concentrated in one place, excessive salt leaches into the soil, creating a harmful environment for plants. Spreading wood ashes in a thin layer over your lawn is a safer application than to use them in your garden, where they are more likely to be concentrated in the soil. Be aware of several precautions if you use wood ashes:

• Don’t apply wood ashes to acid-loving plants such as blueberries, rhododendrons, and azaleas

. • You may have problems with potato scab, a fungus disease, if you use ashes where you grow potatoes.

• Don’t add fertilizer containing nitrogen in the form of ammonium immediately after adding wood ash; the presence of ash can result in the loss of ammonia

. • Don’t add fresh ashes to newly germinated seeds.

Some types of ash are not safe to use on plants, including coal ashes, ashes from lead-painted or chemically treated wood, and ashes from fireplaces or incinerators where trash has been burned.

• Don’t use ashes where soils are naturally high in potassium and soil pH.

• If the potassium soil test value is above 600 ppm, do not apply wood ashes for 5 years.”

I hope this is helpful.