January 30, 2010

1 - Those wood ashes from winter are not good for New Mexico gardens.

Yard and Garden - January 30, 2010


We live in Northern New Mexico and heat our house with wood, everything from willows to cottonwood to juniper to pinon and scrap lumber. We end up with lots of ash that I have been taking to the dump. We are completely organic and make our own compost from vegetable scraps, grass clippings, manure and straw. Can we use the ash in any way in our gardens. We have flowers, vegetables and fruit trees.

- Hamilton B.

Arroyo Seco, NM


I understand your desire to put the wood ashes to good use, but wood ashes are one thing that we must recommend that you do not put into your garden. Ashes are beneficial when applied to soils in regions with high precipitation because the minerals in the ashes replace those leached away by the rains. I checked with Dr. Robert Flynn, NMSU Extension Agronomist, who is familiar with soils in all parts of New Mexico. He agreed that you should not apply the ashes to the landscape or garden. Most New Mexico soils are calcareous (high in calcium and other minerals) as a result of our arid environment. The minerals have not leached away in rains like those in the soils in eastern parts of the U.S. and soils in other regions with much more precipitation than we experience. Adding ashes adds more mineral salts to a soil that already has too many mineral salts. This would create problems for most garden and landscape plants.

In many New Mexico communities discarding ashes in garbage is prohibited to protect the garbage trucks and landfills from live embers. The rules make no exceptions, even for year old ashes. This creates a new problem, you are prohibited from discarding ashes with the garbage, but you should not put these ashes into the garden or landscape. When disposal is impossible, the ashes can be spread very thinly in areas with vegetation that can tolerate them (sagebrush and some other native vegetation). Another option is to spread the ashes thinly over a gravel driveway and in low areas where surplus rainwater collects and will leach the salts away from plant roots. However, the vegetable garden and cultivated landscape are places to avoid disposing of ashes. This is not a way to put the ashes to use, but it is a method to minimize negative impacts from the ashes.

This information is for New Mexico in general. If you live in a part of New Mexico that has greater precipitation, before you put the ashes in the garden, have your soil tested. The pH (acidity) and salt levels of your soil should be determined. When you submit your soil sample, make a note that you want to know if you can apply ashes to your soil. Your local Cooperative Extension Service office can provide you with information about soil testing and help you interpret the results of the soil tests.

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!