The Question
So I'm doing my research on soil amendments, (still for the same article) and I'm reading up on wood ash, and I see this: "they can also be a source of heavy metals that you don't necessarily want in your garden." Damn straight. But was it true? (If you just want the answer, go to the end of this post, Results, Conclusions, and Celebrations.)
That quote came from about.com's gardening site, and in this short article Marie Iannotti ended up taking the reasonable position that "a small amount of wood ash will add some nutrients and be beneficial to most soils," but that "Large amounts should be avoided."
Still–heavy metals? They're almost as scary as cancer these days. And since I've been using wood ashes for several years, I have a real investment in this. Also, I'm doing research, ya know, and when I do research, I mean, I DO it.
(One of my rules is to cite only government and university sources. Not that they're infallible–ha!–but since I'm trying to promote organic techniques, I figure I'll convince noone if I cite green organizations.)
In Search of an Answer
I dug around some. Fingers a-tremble, I typed "wood ash fertilizer" and fearfully scanned the results. One, a study by the Finnish Forest Research Institute, said that "Migration of heavy metals into plants is reduced when their solubility is reduced. Increased soil pH prevents metals from dissolving. Wood ash increases the pH value of soil, reducing acidity." Ash means higher pH which means fewer heavy metals in crops. Whew. Furthermore, they concluded that, in the particular soils they worked with, "wood ash does not accumulate metals in edible berries and mushrooms" even fifty years later. This was what they call a long-term study.
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