People have asked about some of the stuff in my preferred soil mix (mixed finished compost with some composted manures, expanded shale, a bit of coir fiber--probably the percentages are 60%/30%/10% of the pile.)

Expanded shale (ES)is a "puffed" rock that is stable (like lava rock), not crumbly (like vermiculite). It is incredibly lightweight (for a bunch o' rocks...) ES can hold water, nutrients, and a constant supply of air (30% of storage capacity is air). This keeps plants from drowning in clay soils or drying in sandy soils, and is generally helpful for annual-type garden beds. (That is most of our food plants, except for perennial herbs, fruit trees, etc.)

Texas A&M did some studies, and we can understand at least parts of the reports. The American Society for Horticultural Science also has posted a study we can understand pretty well. (Basically, expanded shale works, and pile on the compost, heh.)

The best part of expanded shale as an amendment is you only buy it one time--ES remains in the soil and keeps working. You can probably add a little shale at a time to your soil, up to a total of about 30% (a scant 1/3). I expect that ES will help any annual plant/veggie garden, particularly in stressful weather/moisture conditions or in cases of poor soil.

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AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE

The Use of Expanded Shale in Landscape Mixes

http://www.ashs.org/resources/horteducator/Sloan.html

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A&M Studies (search for A&M, almost halfway down the page):

Resources and Information

Click Here to download A&M Study "NUTRIENT AND MOISTURE DYNAMICS IN EXPANDED SHALE"

[The last couple of slides give the good news]

Click Here to download A&M Study "Evaluation of Expanded Shale in Landscape Mixes"

[Most of this slideshow makes sense to us gardeners--more good news for veggie beds]

GENERAL NOTE: This is primarily aimed at clay soil issues, but the storage capacity of the stuff works in all soil types. A major key here is the search for a permanent amendment that won't break down (decompose) in the soil. Expanded shale replaces vermiculite (and the soggy nature of the peat). You still need to keep renewing the compost part of your soil, either as Mel's "scoop per square" or by another method, such as a 3- or 4-inch layer of mulch that is slowly worked in to the soil as you garden.

http://www.txi.com/products/esc/esc.html

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Expanded Shale, Clay & Slate Institute

The Advantages and Uses of Structural Lightweight Aggregate

http://www.escsi.org/index-old.htm

DETAILS:

ESCS is environmentally friendly. It is non-toxic, odorless, 100% inert, and completely inorganic. ESCS will not compress, degrade, decompose, or react with agricultural or horticultural chemicals. It acts as an insulator in the soil mixture and protects plants from rapid temperature extremes. ESCS retains a high percentage of its weight in absorbed water and waterborne nutrients, making it an excellent buffer. ESCS is user friendly because it is lightweight, inert, pH adjustable, easy to handle, economical and readily available.

http://www.escsi.org/Horticulture%202/Horticul.htm

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MC Magazine

Expanded Shale, Clay and Slate

http://www.precast.org/publications/mc/2003_summer/aggregates_sidebar_1.htm

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Expanded Shale, Clay & Slate Institute

Horticulture Projects

http://www.escsi.org/Projects.asp#Horticulture

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Designer Dirt

WHAT IS Designer Dirt Expanded Shale Soil Conditioner?