WOOD ASH IN THE GARDEN

I just received an e-mail asking whether it’s a good idea to use wood ash in the garden — seems an appropriate topic for a quick blog, what with fireplaces and wood stoves in use once more.

The short message is that wood ash can be beneficial — it contains the macronutrients phosphorous and potash in significant amounts as well as some of the micronutrients and is relatively “pure” so long as you don’t burn cardboard or color-inked paper or other contaminant materials along with the wood.  Wood ash can have drawbacks, too — its composition varies a lot with what kind of wood you burn, the calcium content can raise a close-to-neutral soil pH to too alkaline, it loses nutrient value if allowed to get wet, and it can’t be left in piles or used too often where it will leave too many salts that can harm plants.  And how much to use is the $64,000 question.  I found four different recommended application rates in four different sources.  So, make sure you know (a) your soil is sour enough to warrant application by testing its pH, and (b) what plants NOT to use ashes on.  (The moral to this last bit is “be careful what you ash for”.)

I won’t rehash material already clearly worded and readily available.  Of the sites I visited I think two are the best:

http://www.hort.purdue.edu/ext/woodash.html

http://extension.oregonstate.edu/news/story.php?S_No=34&storyType=garden