From: pharvey@quack.sac.ca.us (Paul Harvey)
Subject: Re: Preparing Clay Soil for Planting
Organization: The Duck Pond public unix: +1 408 249 9630, log in as 'guest'.
Date: 3 Jan 1993 05:29:37 UTC

In article <1992Dec29.184101.19659@gvl.unisys.com> 
garyp@rmtc.paramax.com (Gary Palangian [RMTC/ISP]) writes:
>Hey Now Everybody,
>    Construction on my new house will be complete in a couple of
>months.  My family has all kinds of grandiose plans for the
>backyard landscape.  The house is in the Denver, CO area and
>the soils are very heavy (a lot of clay).  To make matters
>worse, the builder removed and discarded the top
>18" of soil during construction.
>I want to plant bare root trees in the Fall of '93.  I want to
>do flowers and shrubs and vegetables and stuff in
>Spring of '94.  I have read a lot of books that talk
>about amending the soil with peat or manure.  They say
>to add in up to 50% of organic material and till it
>under anywhere from 6" to 24".  These books also make
>it sound like you do this in a weekend.  

Yeah, right. A clay soil is miserable, there is *no* miracle cure. First
off, are you sure you have clay? And what's below the surface clay? Dig
a deep pit, say to six feet and look for a change in soil type or
bedrock, or go to your local library and ask for local soil surveys. 

Ammendments for clay soils? Not peat! Peat is water and nutrient
retentive like clay. What you need is better drainage. Peat is the
prefered ammendment for sandy soils, it is largely a waste in clay
soils. And 6 to 24 inches? You'll need about 4 feet for vegetables,
deeper for trees. Raised beds are the way to go for vegetables. For
trees, you will have to provide drainage. To see if you have a drainage
problem, dig a hole the size of the tree you will be transplanting, roughly
twice the size of the roots or rootball. Fill with water and let drain
completely, then fill again. If the second fill does not drain
completely within 24 hours, you have a drainage problem that will kill
most trees from a lack of oxygen at the roots. The problem is solved by
planting above ground level with garden loam soil or by draining with
drainpipe to a lower sight. In my experience, the best ammendment for
clay soils is ground fir bark mulch or rice hulls up to 50% to a depth of
at least 4 feet. Compost is also commonly used, but is not as stable as
ground fir bark mulch or rice hulls and must be added on a continuing
basis and compost levels beyond 20% will most likely result in bug
problems.

Another problem on clay soils in arid (less than 20" annual rainfall)
areas is salt buildup in the soil. There is a miracle cure for low
levels of salt buildup: gypsum. If you fail the perc (perculation) test
above the first time, try scratching gypsum into the soil in the hole
after the water drains and fill again and see if the drainage is
improved. If it is, then your soil will respond to gypsum. Gypsum is also
the neutral source of sulfur and calcium. For acid soils, add lime for
most plants. For alkaline soils, add sulfur for most plants.

Never work clay soils when soaking wet. Working dry clay soils requires
a jackhammer and produces a lot of dust. In many areas, farmers are
delayed in spring because they have to wait for the soil to dry, not
because of frost. And smart farmers are on loamy soils, the situation is
far worse on clay. Working a clay soil, or any non-sandy soil, when too
wet destroys the structure that holds air in the soil and produces poor
quality bricks and dead plants.

Or, discover the plants that were native to your site and re-establish
them. Your library most likely will have info on native plants.
Newsgroups: rec.gardens