June 16, 2012

1 - Forest fire ash that fell in your landscape and garden should not be a problem unless it is very thick, then you can remove some of it.

Yard and Garden June 16, 2012


So far the fires have not burned on my property, but a lot of ashes have fallen on my landscape and garden. I have read that wood ash in not good to add to garden soil. Is there anything I can do to prevent the ashes from harming my soil?


You cannot prevent the ashes from falling on your soil and unless they collect in layers that are several inches thick, you probably do not need to worry about them. If you do have thick layers that you can collect and disposed of in non-critical parts of your landscape that may help. Wet them down after moving them to prevent them from blowing back into other areas.

The problem with ashes is that they increase the mineral salt content of our soils that already have an excess of mineral salts. This may alter the pH (acidity) of your soil making some minerals unavailable to your plants.

You can counter the pH change by adding organic matter and agricultural sulfur to your garden and landscape. This may be needed in areas with non-native plants, or where ash and mineral salt accumulations are extreme.

Sulfur and organic matter increase the acidity of soils. This allows minerals to more readily dissolve in water and be leached from the root zone of your garden and landscape plants.

As you noticed, water is an important element in this soil remediation if salts have accumulated. We should use water wisely, but if root-top runoff is directed into areas with mineral salt problems, you can reduce the use of purchased (city, water-system, well-produced) water for remediation. It is also important that there be adequate permeation of water through the soil when leaching excess minerals. Without good soil permeability and drainage, the mineral salts cannot be leached from your soil.

For gardeners who have been unfortunate and had fires burn over their properties, they should consider sulfur and organic matter to bring their soils back to productivity as soon as possible. In cases of extremely hot fires, the organic matter in the soil may be burned away; leaving a soil that compacts easily and sheds rainwater and irrigation. If you replace the organic matter with its high water and nutrient-holding capacity and its ability to improve soil structure, you can reduce erosion and restore soil productivity quickly.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!