Carl e Roberts wrote:
15 yrs ago I added 24 cu yds of white sand to my yard (here in
Memphis). (The neighbors thot I was building a beach).
The sand is still mixed with the clay but the
clay still "hardpacks" after a good rain. I have two compost piles
"working" and intend this fall to incorporate large quantities of
organic matter (grassclippings/shredded newspaper) into this garden
spot. My question is this: I am wondering whether to add more sand to
help with the breakup of the clay or maybe gypsum is the answer here-
I am not very familiar with this product what exactly is "gypsum" and
how/when is this product added? where can gypsum be purchased?

I don't know about gypsum but I have heard that clay+sand=cement.

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Travis in Shoreline (just North of Seattle) Washington
USDA Zone 8b
Sunset Zone 5