On Jul 26, 6:10�pm, "David E. Ross" wrote:
On 7/26/2009 9:23 AM, BrucUK wrote:

I have a lawn with clay underneath that floods every time it rains; it's
also full of tree roots.
I have killed the lawn off, built "edges" and a deck/pier to walk
around on. I plan to top-dress the old (now dead) lawn with homemade
compost and well-rotted horse manure to a depth of about 6 inches,
thereby introducing organic matter, and avoiding having to dig too
much. I have "loosened" the soil where possible.
Any thoughts? Anything wrong with this approach? I will not start
planting until next year (herbaceous shrubs, roses and annual
vegetables).
Is this a sensible strategy? Have I missed anything?
Thanks - Bruce

If you create an area with strata of unlike soils, you will find that
plants will not thrive. �Roots of your shrubs and vegetables will not
readily grow through the interface between strata. �Water will not
penetrate through the clay, and you will still have some flooding.

I suggest that you broadcast gypsum over the area, creating a 1/4 inch
coating over the soil. �Lightly water the gypsum to start it dissolving;
then water it into the soil 2-3 times. �This will help break up the clay.

Then rent a power tiller. �When the clay is slightly moist (definitely
not wet), till the area to a depth of two feet. �Top dress with about 3
inches of your homemade compost and well-rotted horse manure. �Till
again to a depth of a foot. �Then top dress again with another 3 inches
of the compost and manure. �Till one more time to a depth of only 6-9
inches.

If you don't walk on the area when it is truly wet, you won't have to
work the area for several years. �You will also find that plant roots
will eventually grow well below the depth that was worked. �However, you
might have to spread more gypsum annually to replace what has leached
away; this will keep the clay porous and well-draining.

--
David E. Ross
Climate: �California Mediterranean
Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean
influence (USDA 10a, very close to Sunset Zone 19)
Gardening diary at http://www.rossde.com/garden/diary

This sounds like the best plan except that I would grow a deep rooted
cover crop for a couple months first and then proceed with the
above.