TULSA MASTER GARDENERS - Household Debris (Fireplace Ashes)

We have been told that the summer wildfires were not a complete disaster. The forest will rejuvenate and the ashes will add the nutrients that will make the vegetation even more lush. If this is true in the forest the question becomes, "Can I benefit by using my fireplace ashes on my lawn and garden?"

FIREPLACE ASHES and YOUR SOILLEL
(condensed from OSU Extension FS 2238)

Studies of fireplace ashes have found that of the elements analyzed, available potassium (K2O) was the only nutrient element found in significant amounts. The amount of available potassium ranged from 3.6 percent for hickory, 4.5 percent for oak to 8.9 percent for a mixture of hard and softwoods. The average for the fireplace ash tested was 6.0 percent. The analysis also revealed that the ashes have an acid neutralizing power of about 20 percent of pure lime. Because ashes are more soluble than lime, they will neutralize soil acidity within a few days after incorporation by rain or cultivation. On the downside, the analysis indicated the ashes contained a salt content of about 22 percent.

Can I use it?

If your soil has a neutral pH (pH near 7) or has adequate potassium then ashes should NOt be applied (this is normally the case for urban settings with standard fertilization programs.) However, if your soil is acidic AND moderately to severely deficient in potassium the application of ashes may improve the soil. Only a soil test will give a definitive answer.

How do I use it?

The safe amount of ashes to be applied will depend on the soil type. For sandy soils the maximum rate of 10 gallons of ashes per 1000 square feet will supply 3 pounds of K2O and 10 pounds of lime. For all other soils the maximum rate of 20 gallons per 1000 square feet will supply 6 pounds of K2O and 20 pounds of lime.

If you should decide to apply ashes to your garden or lawn please follow the following guidelines as supplied by the Oklahoma Cooperative Extension Service:

Care should be taken to measure the area of the lawn or garden to which ashes are going to be applied and to know exactly the volume of the bucket or other container used to measure ashes for the application. Excessive applications may ruin the soil. Areas treated at the above rates should not be retreated again for 10 years or until a soil test shows a need for lime or potassium again. To avoid repeat applications to the same area, sketch the lawn or garden area to be treated. Then, as ashes are applied, the treated area can be shaded in or otherwise marked. 1

 

Sources:
1. Oklahoma State University Extension Facts F-2238, Fireplace Ashes for Lawn and Garden Use, by Gordon V. Johnson

Need More Help?

Walk-ins are welcome at the Master Gardeners office at the O.S.U Extension Center, 4116 E. 15th Street (Fairground Gate #6). You can reach us by phone at (918) 746-3701. Our hours are from 9:00 a.m to 4:00 p.m. Monday through Friday.

Oklahoma State University Cooperative Extension Service offers its programs regardless of race, color, national origin, sex, religion, age or handicap, and is an equal opportunity employer. Work in Agriculture, Home Economics, and Related Fields, USDA, OSU and County Commissioners Cooperating.

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