Answer: Wood ashes are a traditional source of potash and to some extent phosphorus, however their fertilizer value varies based on the type of wood burned; they also tend to leach very quickly which means they can "burn" tender plants. Finally, they are alkaline and should not be used around acid-loving plants such as azaleas. If you opt to use them, you could perhaps use them as a side dressing (keeping them several inches away from seedlings or newly planted plants) at a rate of about 5 pounds per 100 square feet; as a rough guide hardwood ashes would be about 10 percent potash. (Do not use coal ashes, by the way.) Sprinkle them lightly or push them through a sieve to achieve even coverage. Reduce the use of other sources of potash accordingly.
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