Re: [tomato] blights

Thomas Giannou (
Wed, 28 Apr 1999 23:29:57 -0700

Dear Olin,

The P in the Rock Dust sample sent to me is rated at .003%.  There is a fair
amount of Iron and Zinc present.  There are 50+ minerals present in the Rock
Dust.  As for Rock phosphate and alkaline soils, a bacteria that soubalizes
phosphates or VAM fungi can also get at that kind of phosphate.  In this
product, the phosphate level is too low to be of a lot of use.  Many other
minerals are present and are useful to a variety of plants.  I think the
main emphasis of Rock Dust is to furnish all kinds of minerals to plants....
the net effect, claims the manufacturer, is to increast plant health and
yields.  The increased health helps the plant resist diseases and other
problems.  It should be interesting to hear what the Washington State
Department of Agriculture Fertilizer Division has to say about the heavy
metals contained in this particular Rock Dust product.  That's the only
thing that I am conserned about with that stuff.  I am not sure I want to
stock Rock Dust anyway.  I will take a look at the reference you gave....
thanks for taking the time to look that up.

Thomas Giannou
Spokane, Washington
-----Original Message-----
From: Olin <>
To: <>
Date: Wednesday, April 28, 1999 6:12 PM
Subject: Re: [tomato] blights

>Rock phosphate is so insoluble in alkaline soils that it is of little or no
>value as a source of plant available  phosphorus.  I was assuming rock dust
>to be a powder form of rock phosphate (not certain if that is so) and it
>would also be insoluble.  It is probably great for acid soils.  There was a
>thread on this topic 2-3 years ago on
>the U of A arid_gardener listserv.  The final word is from the U of A soils
>department archived at
>   As you suggest,
>mineral depletion is not a normally problem in our desert soil with the
>possible exception of iron and zinc (required by citrus) which are
>in some areas.  -Olin
>-----Original Message-----
>From: Thomas Giannou <>
>Subject: Re: [tomato] blights
>>... why would rock dust be inappropriate to desert soils?   ... Perhaps in
>your soils mineral
>>depletion by plants may not be a problem?   .../