Granite Dust
Wed, 09 Nov 2005 20:42:39 PST
I have never written here before, although I've been reading all your 
posts with interest for quite awhile. However, I felt compelled to 
pipe in a few comments on the rock dust discussion.
Last year I wrote two papers for my soils and plant propagation class 
on rock dust, after coming across information on it and being 
intrigued with its possibility. I searched for studies done with rock 
dust and became more intrigued the more I came across. I will try to 
give you a succinct impression of what I learned.
The obvious first thing one must remember is that the soil we have 
was created by rocks in the first place, particularly in the Ice 
Ages, when the movement of rocks enhanced soil throughout the world. 
Rock dust is a 20th century byproduct of the quarry industry, which 
is generally considered to be a waste product.
  In terms of its benefits, they are the following: it improves soil 
hydrology, buffers acid soils, and can provide potassium to plants on 
demand. According to the studies I located, it can restore lost and 
trace elements to the soil, increase the nutritional value of food 
crops, increase product yield, increase plant resistance to insects 
and disease, enhance microbial activity, aid soil moisture retention, 
aid the development of better root systems, reduce plant mortality 
rate during transplant, reduce the plant's need for soluble chemical 
fertilizers...there's a lot more, but you get the idea.
It is very stable, dissolves very slowly and remains active in soils 
for many years, making it very cost-effective. It can be gotten for 
next to nothing at any local quarry.  It is not a fertilizer in the 
usual sense of the word; it contains no nitrogen, very little 
phosphorus and a tiny amount of potassium.
The most recent study I'm aware of is in Scotland, where the 
government has invested $100,000 in a three-year study combining 
compost and rock dust. Studies have also been done in Australia by an 
organization called Men of the Trees, who did a fascinating and 
successful trial using tree seedlings: in it, every tree species 
grown was twice as tall as the control plant, growth rates were up to 
five times faster than without rock dust, tree seedlings with rock 
dust appeared to resist insect predation, and there was a noted 
absence of fungal attack in the early stages of seedling growth. 
They now use 5 grams of rock dust for each tree seedling they grow.
The amount to add per plant seemed to vary a great deal depending on 
what I was reading, and I found this somewhat confusing. It seemed to 
vary from 14# to 50# per hundred square feet if you are broadcasting 
it. In pots perhaps 5 grams per plant/bulb? This is a guess.
If anyone is interested--and I hope this contributes to the 
discussion of bulb health rather than appearing to be a tangent on 
something else entirely--I'm happy to copy and paste one or both of 
the papers I wrote and send them on.
If you are in the San Francisco Bay Area, Common Ground in Palo Alto 
sells Spiral Stonemeal for $18/50# bag.

Jean in San Francisco


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