Soil amendment

Asked May 29, 2020, 5:48 PM EDT

I have a place on my 5 acre farm that I always do my woody debris burn pile. Recently, after an all day burn, I looked at the soil and it looks amazing. Could I amend my flower garden soil safely with that soil?

Washington County Oregon

1 Response

Thank you for choosing Ask an Expert for help with your question on using soil with a high amount of wood ashes. And here we are talking about ash of actual woody debris from plants, not treated or painted wood.

Wood ashes do contain nutrients, most prominently potassium. Knowing the potassium level in your soil would be helpful; you don’t want to over-do it. Wood ashes are quite alkaline, and knowing whether your soil is more acid or more alkaline is also important, when considering adding them to a garden bed.

The “color kits” sold in nurseries can give you an estimate of your soil pH. For a more accurate reading and for nutrient levels, check with a laboratory. Find one in the publication “Analytical Laboratories Serving Oregon” See here:

All that said, a moderate use of wood ashes can be appropriate. Hardwoods contain about five times the nutrients of softwood, so keep that in mind, over all.

Here are some guidelines:

Scatter the ashes or soil mixed with ashes. Placing them in piles or rows can concentrate the nutrients and burn roots.

Do not use high alkaline materials on acid-loving plants--blueberries, rhododendrons, azaleas, etc.

Avoid using concentrating ashes around newly-planted seeds.

A longer discussion on using wood ashes in the garden can be found in the Oregon Extension publication Fertilizing Your Garden: Vegetables, Fruits, and Ornamentals. See here:

Have a great gardening year,