On 12/2/2015 2:36 PM, Bob F wrote:
David E. Ross wrote:
On 12/2/2015 7:44 AM, Bob F wrote:
David E. Ross wrote:
Today, I went to buy gypsum to apply to my clay soil before the
winter rains begin. While I never buy plants at a hardware store
or lumber yard, I do buy tools and supplies at such stores.

I went to a nearby hardware store (about 3 miles from my house) and
took a 40-pound sack of gypsum to the register. With a
senior-citizen discount of 5%, the clerk said that it would be
$12+change. I left the sack at the register and drove to a
favorite nursery about 12 miles away. There, I bought a 50-pound
sack of gypsum for under $9.

That is correct: 25% more gypsum for 25% less money. Both were 92%
CaSO4 (calcium sulfate).

What effects do you see from applying gypsum? Is it anything
obvious? Are repeat application useful?



My soil is very heavy clay. Gypsum supposedly reacts with the clay to
make it porous and thus improve drainage and root growth. I apply a
generous amount annually in the late autumn around my camellias,
azaleas, and liquidambar tree, which seem to thrive. Every two
years, I apply it throughout my garden, using about 250 pounds.
Also, when planting a new plant or bulb, I stir a small amount of
gypsum into the planting hole.

My sister tried one application a year ago on her lawn because of standing
water/sogging ground problems and has really seen little change. I could give
her more (someone else gave me) if it would do any good. Just wondering.



If the cause of your sister's problem is from a high water table or very
thin soil over bedrock, gypsum will not help.

--
David E. Ross
Climate: California Mediterranean, see
http://www.rossde.com/garden/climate.html
Gardening diary at http://www.rossde.com/garden/diary