Wood fires mean ash. Before spreading it in garden, take these steps for sake of soil

Local gardeners are always searching for a magic concoction that will quickly and easily improve our heavy clay soils. While a clay base is highly nutritious, it is difficult to manage. The best way to improve our soils is with the addition of organic matter.

During the winter months many people have an ample supply of wood ash from building a cozy fire. One garden myth is that wood ash makes an excellent soil amendment. It is organic after all. Before applying fireplace ashes to garden soils, understand that the benefits may not outweigh the risk.

It has been said 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.

Here is the potential problem. Local soils are usually naturally high in potassium. Adding more may not be beneficial. Additional potassium will elevate the level, which means you run the risk of saturating the soil. The result is the other micro-nutrients found naturally in the soil necessary for plant growth become unavailable to plants.

There is another potential issue with wood ash. Ash tends to be high in pH. The spread of wood ash on our local soils raises the pH level. Our local soils already tend to run on the high side. The addition will continue to increase the pH over time, which reduces nutrient availability and results in a decline of growth.

The bottom line is wood ashes add little benefit to the soil and may cause more harm than good.

So how do you dispose of the ash without putting it in the trash? The key is to spread the ash far and wide to dilute their negative properties. Ash can be added to the compost pile where it will be defused and continue to break down. Sometimes the more acidic nature of the compost can offset the higher pH of ash. However, home compost tends to have a higher pH and greater quantities of ash in the compost will continue to raise the pH.

Ash can be lightly broadcast over the lawn where the concentration would be reduced. Continued applications to the same area year after year will result in problems with the soil.

A soil test offered through your local county Extension office is beneficial. The test determines the pH of your soil. This will let you know if your pH is already naturally high, which means ash should not be applied. Alternatively, it might be on the lower side and applications may not harm the soil.

The cost of a soil test varies by each county but is usually provided for a minimal fee. Johnson County residents are encouraged to take advantage of a free routine soil analysis which tests the pH, phosphorus and potassium levels of the soil, offered by Johnson County K- State Research and Extension through a grant with Johnson County Stormwater Management. The result of the test provides base-line fertility levels for a healthy lawn and garden. This not only helps to manage pH but also offers guidelines on when and how to fertilize. https://www.johnson.k-state.edu/lawn-garden/soil-testing/free-soil-test.html

For those who burn wood from time to time, the broadcast of ash over larger areas 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 to keep it out of the waste stream.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Have a question for him or other university extension experts? Email them to garden.help@jocogov.org.

This story was originally published December 23, 2022 at 6:00 AM.