[permaculture] On a Fad Diet of Rock Dust, How the Garden Does Grow - The New York Times
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On a Fad Diet of Rock Dust, How the Garden Does Grow - The New York Times
On a Fad Diet of Rock Dust, How the Garden Does Grow
By HENRY HOMEYER
JUNE 24, 2004
FOR years I had been hearing about the virtues of gardening with rock
powders. Two summers ago I gave in, acquiring some finely ground granite
from a company that engraves tombstones. I scratched the stuff in around my
Although it was August, the plants were small and appeared to be sulking.
By mid-September I needed stakes to keep them from tipping over from the
weight of the fruit -- a first in my 20 years of growing peppers in chilly
Joanna Campe, just down the road from me in Northampton, Mass., has been
folding rock powders into her garden soil since the mid-80's, when she came
across the work of an engineer turned farmer and writer, John D. Hamaker,
who argued that rock dust could mimic the action of soil-enhancing glaciers.
''If we imitate how the earth forms soils, we need to give our gardens more
than just the three elements found in chemical fertilizers,'' Ms. Campe
said, suggesting they need close to 90 minerals.
Like Mr. Hamaker, Ms. Campe believes that over the millenniums the soil has
been depleted, leaving the food chain deficient in important trace
minerals. For centuries people in the remote Hunza Valley of Pakistan
farmed soil irrigated by ''glacial milk,'' routinely living to be 100.
Other factors were of course at play, but rock powder enthusiasts theorize
that the health and longevity of the Hunza people were related to the
plant-borne minerals in their diet.
Continue reading the main story
Continue reading the main story
I was intrigued. So after my pepper explosion, I added granite powders to
half of my potato plot, following Mr. Hamaker's recommendation of about 14
pounds of rock dust per 100 square feet of garden bed.
At the beginning of the growing season, the potatoes with rock powders grew
like sprinters leaving the starting block. They were six to eight inches
tall when the others had reached two to three inches.
The action of the powders was a bit mysterious. Rocks contain no nitrogen,
the fuel for fast green growth and one of the three components of chemical
fertilizers. Although they may contain some phosphorus or potassium, my
soil tested more than adequate for both, so they were not correcting a
Dr. John M. Duxbury, a professor of soil science at Cornell University,
pointed out that common soil treatments like limestone and phosphorus
started out as rocks -- as did soil in general. But he was not convinced
that rock powders raised the quality of soil already treated with
fertilizer. ''In the tropics we use rock phosphate because it is cheaper,''
Research in the tropics by Dr. Ward Chesworth, an emeritus professor of
land resource science at the University of Guelph in Ontario, found that
rock powders did indeed improve the productivity of soil deficient in
minerals because glaciers never got that far. When asked about my potatoes,
Dr. Chesworth said they may have benefited from acids around the roots,
which possibly broke down the minerals and made them easier to absorb.
But even in New Hampshire, he suggested, soil could lack trace minerals,
because farmers have been ''making tea with the same bag for 10,000 years.''
Though there are few field trials to prove the rock powder case, anecdotal
evidence abounds. After using rock powders at her nursery in Claremont,
N.H., for 10 years, Susan Lawrence said, her hostas became more
disease-resistant and winter-hardy, and better bloomers, too.
That leaves gardeners like me experimentally dusting their plots with
ground granite, basalt or other rocks. Luckily, these powders, also called
rock fines and rock flour, are inexpensive -- often free -- from quarries
and rock-crushing plants. (Sources are listed on Ms. Campe's Web site,
Last fall, with winter breathing down my neck, I harvested my potatoes
without stopping to compare the weight of those grown with and without rock
powder. This year, I treated the whole garden. And who knows? Maybe that
extra dash of minerals will help me, like the Hunza farmers, live to be 100.
Remineralize the Earth
...better soil, better food, better planet.
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