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Archive for Sunday, December 28, 2003

Wood ashes in most soils ineffective

December 28, 2003

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Although the mild winter temperatures have been good for heating bills, many people have been able to enjoy the sights and sounds of their wood fireplace.

The snap, crackle and pops add a cozy, warm feeling to family gatherings. But after the hot embers cool, and a pile of ash remains, homeowners wonder what to do with all those ashes. A simple and convenient solution is to dump them on the flower bed or vegetable garden. This, however, may not be the best use for such potentially hazardous material.

Here are some hints to help you safely dispose of large quantities of fireplace ashes:

Wood ashes are a predominantly carbon-based material that contain no nitrogen or phosphorous. Both nutrients are lost during the burning process. The only useful nutrient in wood ashes is potassium. Unfortunately, most local soils have high levels of potassium and extra potassium is unnecessary. In fact, potassium is stable in the soil and does not leach out. The only way it is lost is by plants using it for growth and development. This is why a soil test is recommended before adding nutrients. It is difficult to know what is needed when you do not know what is already available.

Another problem is that wood ashes function like lime to increase the soil pH. pH is a measure of soil acidity or alkalinity. Again, in our area, soils are calcareous or derived from native limestone. The pH is mostly neutral, so lime is generally not needed. By applying large quantities of wood ashes to the soil, you may raise the pH to an undesirable level. The result would be plants that are pale green, weak and not productive.

The benefits of wood ashes in most garden soils is not all that great.

To use wood ashes to their greatest potential, mix them with the compost pile to create a more balanced "fertilizer" type product.

The high levels of potassium will complement the nutrients already found in the pile. Likewise, composting can create acid. Applying wood ashes will neutralize the acid and will raise the pH to a more neutral level.

If you do decide to apply wood ashes directly to your garden or flowerbed, spread them in a very thin layer. Avoid piling them up in a concentrated amount. Likewise, rotate the areas that you apply them to. If routinely spread in the same area, they could adversely influence the soil pH and nutrition next year.




Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.

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