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Using wood ash to improve soil

Relaxing hours spent by the wintertime fire produce a lot of wood ash; should you put those ashes in your garden this spring?
Relaxing hours spent by the wintertime fire produce a lot of wood ash; should you put those ashes in your garden this spring? The Kansas City Star

When it comes to improving the soil, local gardeners are always looking for that magic bullet. One old wives’ tale is that wood ash makes a great soil amendment. But before applying fireplace ashes to the garden, take caution.

The general thought is, wood ashes incorporated into your garden will help make the soil more fertile. Though ashes do contain significant amounts of potassium or potash, they contain little phosphate and no nitrogen.

Most local soils are already naturally high in potash and do not need more. Adding more potassium will elevate the level, which means you run the risk of saturating the soil. The result is, other micro-nutrients needed for plant growth and found naturally in the soil become unavailable to plants.

Another problem is that wood ash raises the pH level of our soils. Our local soils, for the most part, tend to run on the high side. Adding ashes over time will continue to increase the pH which will reduce nutrient availability and result in a decline of growth.

The bottom line is that wood ashes add little benefit, and may actually harm many local soils. So how do you dispose of the ash without putting it in the trash? The key is to spread them out and dilute their negative properties.

Ash can be added to the compost pile where it will be defused and continue to breakdown. Sometimes the more acidic nature of the compost offsets the pH issue. A small amount of ash can be lightly broadcasted over the lawn where the concentration would be lessened. The real problem lies in continued applications to the same area year after year.

For those that burn wood from time to time, broadcasting is the best method of disposal. If you burn a large amount of wood then you may need to get more creative about where to apply the ash.

Dennis Patton is a horticulture agent with the Kansas State University Research and Extension. To get your gardening questions answered on The Star’s KC Gardens blog by university extension experts, go to KCGardens.KansasCity.com.

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