Saturday, December 17, 2016 By: Ask A Master Gardener

Be Careful When Using Fireplace Ashes in the Garden

Fireplace ashes can harm gardens

Bill Sevier: Ask a Master Gardener

Saturday, December 17, 2016

Q: Is it OK to spread my fireplace ashes over my vegetable garden every winter? N.G., Sand Springs.
A: The best answer is “probably not.” Ashes from burning various types of wood have a unique chemistry, which might be useful in some situations but are not recommended for vegetable and ornamental gardens or for lawns, with few exceptions.
The problem with ashes is three-fold, two of them significant. One is that the pH is high. The pH is a measurement of level of acidity on a scale of 0 to 14, with 7 being neutral, 0 very acid and 14 extremely alkaline. Examples of the pH of some items are: Battery acid pH of 0, lemon juice pH of 2, pure distilled water pH of 7, baking soda pH of 9 and household bleach has a pH of 12-13.
The pH range of fireplace ashes has an average value of 11.6, right up there with household bleach. Added to soil, it removes acid, driving the pH value up and out of the range of acidity that most plants prefer.
Most vegetables and lawn grass perform best in slightly acidic soil of an average pH range of 5.8 to 6.5. Many shrubs need even lower pH values. Azaleas, blueberries and gardenias need an acidic pH of 5 to 5.5. Other acid-loving shrubs include most conifers, camellias and hollies.
When the soil is out of the pH range needed by a particular plant, it cannot absorb nutrients, such as iron. This is the reason for yellow leaves on many azaleas growing in soil that has become too alkaline, producing yellow leaves that have a distinctive pattern called iron chlorosis.
Another downside to using fireplace ashes is the amount of salt. Excess salt in soil will predictably kill plant roots. An example of this is seen with the use of salt on roadways in winter with subsequent death of roadside plants the following spring. Once the salt is in the soil, it may take a long time for correction to occur.
The last concern about fireplace ashes is the amount of potassium. There is about 6 percent potassium in ashes, and they will add this nutrient to soils, which if deficient, could be helpful. However, the results of soil tests of Tulsa-area gardens by OSU show that in previously fertilized soils, the majority have adequate or excessive potassium.
OSU has a fact sheet “Fireplaces Ashes for Lawn and Garden Use,” which offers a good summary of chemical content of various ashes from burning different hardwoods. The fact sheet recommends that if ash is used, one should use no more than 10 gallons per 1,000 square feet in sandy soils and 20 gallons for the same area in other soil types. The key take-home fact from this document is that if you apply ashes to your soil as outlined above, you should do so no more often than once every 10 years.

Garden tips
§  All birds need and appreciate clean feeders and unfrozen water on cold days. Place feeders close to protective shelter, if possible.
§  Select a freshly cut Christmas tree. Make a new cut prior to placing in tree stand. Add water daily.
§  Light prunings of evergreens can be used for holiday decorations. Be careful with sap that can mar surfaces.
§  With the warmer weather, newly seeded fescue will continue to grow roots and make energy if you keep them free of leaves.


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