Posted 21 January 2010. Crop Management.

Wood Ash a Chancy Fertilizer

Source: Kansas State University Press Release. www.ag.ksu.edu

Columbus, Kansas (December 23, 2009)-For generations untold, gardeners have been adding ashes to their vegetable plots as a fertilizer and soil amendment. For them, itīs been a second use for the wood burned in cooking and staying warm.

But, these recyclers havenīt been worldwide. In some regions, continued ash disposal can make soil unfit for crops.

"Kansas can be one of those regions. You need certain conditions for incorporating ashes to work well, and Kansas soils donīt necessarily have them - particularly outside the southeast," said Jake Weber, horticulturist with Kansas State University Research and Extension.

Adding ashes works best, he said, where the soilīs available levels of phosphate and potash are in low range. The soil also should be acidic enough to need a higher pH - i.e., be more alkaline.

"Thatīs much more likely in the northeastern United States than in the limestone-rich High Plains," Weber said. "To avoid problems, Plains residents should have their gardenīs soil tested first, to determine the need for changing pH or adding nutrients."

The horticulturist provided these additional cautions for Kansans who feel compelled to recycle:

• Try to maintain a margin of safety by limiting your annual application rate to no more than 5 pounds of wood ash per 1,000 square feet.

• Stop wood ash applications when the soilīs pH reaches 7 or when its phosphate and potash levels climb into the very high range.

• Do your homework first. In addition to such landscape plants as the hydrangea, heather and azalea, many vegetables and fruits prefer slightly acidic soil - the opposite of what ashes create.

Weber said Colorado Extension has a good list of plants and their preferred pH levels. Links to the listīs groupings of houseplants, woody ornamentals, vegetables and fruits are available on-line at www.coopext.colostate.edu.