[permaculture] Rock Dust

tanya tanyagarden at gmail.com
Fri Mar 8 00:38:33 EST 2013


On Thu, Mar 7, 2013 at 8:32 PM, Chris Carnevale <c.s.carnevale at gmail.com> wrote:
> Hi,
>
> I'm wondering who has used rock dust as a soil amendment and what your
> results were?  Has anyone found a better freely available micronutrient
> source?  How does seaweed compare to rock dust?
>

Haven't used it, but I recently read Steve Solomon's book on growing
nutrient-dense food, The Intelligent Gardener. He says mineralized
basalt rock dust is not practical for backyard gardeners because it's
expensive (to use the amount needed) and takes many years to show a
difference.  He analyzes what specific minerals you get (pounds of
each element per ton of rock dust) and looks at what other sources are
available. Instead of rock dust, he recommends sulfates from Black
Lake Organics for Fe, Mn, Cu, and Zn. They can be added to a dry fert
(based on the results of a specific $20 soil test from Logan Labs) or
used as a foliar feed (using a max of 1 tablespoon of single or mixed
sulfates per gallon of water; i teaspoon max for Cu). For
micronutrients such as Cr Co I Mb Se Sb V Ni   he recommends kelp meal
at 1 pound per 100 sf per year. For B he recommends regular laundry
borax, a teaspoon or so per 100 sf, depending on your soil test. (I
don't own the book but took a few notes.)

I'm in the middle of reading Phil Nauta's book on growing
nutrient-dense food, Building Soils Naturally. He does recommend rock
dust for everyone, but does not go into the details of what it
contains or how long it takes to see results. He recommends 2-50
pounds per cubic yard of compost so that it gets chelated with the
organic matter. For application directly to garden beds, he cites
other recommendations, which vary from 15 to 50 pounds per 100 sf, and
says as little as 0.5 lb/100sf has shown results. He also recommends
kelp meal, at 0.3-1 pound per 100 sf/yr. In addition, he also
recommends ocean water for some of the same trace minerals (and
recommends other additives that act as biostimulants), but again, does
not name the minerals.

Engineers will prefer the Solomon approach, very linear and
numbers-based, with detailed arguments for making each choice.

Kitchen witches will prefer the Nauta approach, lots of brews and biostimulants.

The approaches seem quite different, but depending on your garden and
your goals, I think both approaches lend themselves to experimentation
and are complementary, for the most part. They do disagree on using
ferts with GMOs, and Solomon has a whole chapter about not relying on
compost.

If anyone else has read either or both of these books, I'd be
interested in hearing what you think. I've been thinking of getting my
soil tested (at a community garden plot) and playing around with more
than just the alfalfa pellets, nettle and comfrey teas, and compost
I've been using.


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