From london@ladybird.oit.unc.edu Tue Apr 26 09:16:14 1994
Date: Thu, 21 Apr 1994 23:46:56 -0400
From: Larry London <london@ladybird.oit.unc.edu>
Subject: MAY 91 Wood Ashes As A Fertilizer/Lime Material

MAY 91 Wood Ashes As A Fertilizer/Lime Material
 
With the increase in use of wood stoves for home heating, questions
have arisen concerning the feasibility of applying wood ashes to
supply plant nutrients.  The nutrient content of wood ashes is
variable, but in general they contain approximately 1% phosphorus,
5% potassium, and small amounts of boron and other elements.  In
addition to supplying nutrients, wood ashes have neutralizing
properties similar to limestone.  Although the actual neutralizing
value will vary depending on  hardwood used, in general they have
about one-half to three-fourths the neutralizing value of limestone
(i.e., 20 lbs. of wood ashes = 10-15 lbs. of lime).
 
Wood ashes may be applied to the home garden to supply the above
needed plant nutrients and reduce soil acidity.  Application should
be made ONLY if the soil pH (acidity factor) is less than 7.0,
based on a soil test.  Suggested rates are 10-20 lbs. of wood ashes
per 1,000 sq. ft. per year.  A 10 qt. pail, filled to within 2" of
the top, will contain about 5 lbs. of wood ashes so 2 to 4 pails
may be used per 1,000 sq. ft.  Higher rates should be avoided
because of potential plant toxicity problems.  The soil should be
tested after two years to check for changes in pH, phosphorus and
potassium levels to determine if further wood ash applications
should be made.
 
Wood ashes should not be applied in contact with germinating seeds
or plant roots because of possible salt burn from the potash in the
ash.  To be on the safe side, wood ashes should be incorporated
into the soil before planting using a rototiller or plow.
 
One word about coal ashes - do not use them as they have no
neutralizing power or significant nutrient-supplying properties.
 
Additional Notes - The reason for the 20 lbs. per 1,000 sq. ft. per
year maximum for wood ash application is that wood ashes may
contain 1-3 or more lbs. of boron per ton so a 50 lb. per 1,000 sq.
ft. application (i.e., approximately 1 ton per acre or 1-3 lbs of
boron per acre) is too high for a general recommendation.  Toxicity
problems may develop for some crops.
 
Wood ashes may also be applied to lawns if the chunks of charcoal
are removed.  Maximum rate is 15 lbs. per 1,000 square feet.  If
the turf is actively growing, the wood ashes should be watered in.
 
. . . Steve Donohue