garden soil prep

Jane McGary
Tue, 18 Feb 2003 09:44:00 PST
Cathy Craig asked, 
>In much of Southern California we have clay soil. In certain parts of our
>lot in San Clemente, most notably those areas closest to the house and
>garage, most everything below about 6 inches is pure clay. Not clay-ey, but
>pure grey clay (no soil). In the front yard the people who put in the sod
>applied some gypsum, which did seem to help. I am now working on the beds
>and they need a lot more work than was done to sod the lawn.
>I bought a bag of gypsum today. Customarily I just dig out all the old soil
>and have it hauled away. I am going to try amending some of it but there
>aren't very many instructions on the gypsum bag and no explanation at all on
>how it works or why it works or whether it 'wears out' over time and I will
>have to re-do the whole job again in future.

Here is a quote from the forthcoming "Rock Garden Design and Construction,"
the chapter on soils by Louise Parsons. If Louise is a member of this
forum, thanks are due to her for this excellent chapter, which you will be
able to read in toto next fall when Timber Press issues the book:

"For example, some clays have very specific properties of adhesion,
particularly to the common yet highly variable mineral feldspar. If you
have a clay-feldspar incompatibility, mixing in grit or sand that contains
large quantities of feldspar will produce a nasty concretelike soil. Some
soils are gypsum-receptive, while others are not: adding gypsum, often
recommended by general gardening manuals, does not automatically balance or
even influence pH in all soil types. Still other soils contain a clay that
adheres to gypsum, producing a concrete or crusty hardpan. You can spend a
lot of money on this popular additive, only to make textural problems worse."

Apparently Cathy's soil is "gypsum-receptive." 

There is a great deal of information on making rock garden soils in this
forthcoming book, and I'm sure it will help bulb growers as well.

Jane McGary
NW Oregon

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