[Arid_gardener] Granite as soil amendment

[Dick Gross]

Someone will correct me if I am wrong but I think we are confusing terms. A "soil mix" or just the tern "soil" is a mixture of any materials or "media" in which a plant's roots take residence to extract water and nutrients to build new cells and the hardware to reproduce itself, roughly speaking,

A mulch, on the other hand, is any material--newspapers, plastic, rock, wood chips, any other debris placed on top of the ground, not in, or not as an integrated part of the media in which the roots reside. Organic material mixed into the soil continues to decompose consuming, as it does, nitrogen needed for plant growth. If one is aware of this contrived deficiency, additional nitrogen can be applied to make up the difference. But the condition is suttle and we may mot properly diagnose the problem.

We might mix crushed rock or sand in ground to improve tilth, drainage or aeration but we call it a soil ammendment, not mulch. Mulch is placed on top of the root media for esthetic purposes or to conserve moisture by decreasing evaporation. There is an interaction at the interface between organic mulch and the soil organisms that is beneficial but those organic compounds will have been well decomposed by the time they have gone through the guts of the organisms in the soil.

Whatever one does to soil, it is essential that irrigation water percolate through and out of the root zone flushing salt out and pulling air in behind it. Roots cannot survive without air and we all know the deleterious effects of salt.

This analysis may not be technically correct in every aspect but if anyone is uncomfortable with the explanation, we might all benefit from the additional dialogue.

Dick Gross, Master Gardener Volunteer
University of Arizona
Maricopa County Cooperative Extension  

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----- Original Message ----- 
From: "Chris Trask" <christrask at earthlink.net>
To: <arid_gardener at CALS.arizona.edu>
Sent: Wednesday, October 04, 2006 8:25 AM
Subject: Re: [Arid_gardener] Granite as soil amendment


>     I used gypsum for years to try overcoming the problems of clayish soil, and the results were poor at best.  However, when I worked at the Boyce Thompson Arboretum I quickly learned that the far better long-term solution is to remove the clay by excavating to a depth of a foot or more, and then backfilling with a 1:1:1 mixture of soil, compost/mulch, and coarse sand (1/8 inch sift and smaller).  I applied this method to my own garden, and there has been a tremendous improvement in the establishment of new plantings, seedling emergence, and overall plant health.  
> 
>     You can buy the 1:1:1 mixture from any number of landscaping suppliers, and you may want to do a simple soil test of your own to ensure that the clay content is at a suitable level.  For a 1-gallon planting, you should excavate a volume equivalent to a 5-gallon paint bucket, and after a while the spaces between the plants can be excavated and backfilled as well, which improves the drainage and reduces the occurance of root rot.
> 
> 
> -----Original Message-----
>>From: Bill Woody <billw-9 at msn.com>
>>Sent: Oct 3, 2006 2:45 PM
>>To: arid_gardener at CALS.arizona.edu
>>Subject: [Arid_gardener] Granite as soil amendment
>>
>>Most of the rock and gravel companies sell 1/4-inch washed granite,
>>essentially no fines.  Also, most of them have displays where you can see
>>what it looks like.
>>
>>This is meddling rather than answering your question.  I tend to think that
>>bark or mulch would be better than granite to loosen clays if you want to
>>grow things in the amended soil.  They are also much easier to transport and
>>handle, unless you're a muscular young guy with your own truck.  I'm
>>assuming you have a small plot, not a half-acre.
>>
>>More authoritative responses from the MGs are welcomed.
>>
>>Bill Woody
>>
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> 
> 
> Chris Trask
> Outings Leader, Sierra Club (1981-1991)
> Palo Verde Group Outings Chair, Sierra Club (1985-1988)
> Grand Canyon Chapter Outings Chair, Sierra Club (1988-1991)
> Member, Arizona Native Plant Society
> Member, Arizona Governor's Advisory Council on Invasive Species
> Member, Central Arizona Weed Management Area
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> Arid_gardener at CALS.arizona.edu
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>
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