On 12/2/2015 4:36 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.



The Myth of Gypsum Magic: Adding gypsum to your yard or garden will
improve soil tilth and plant health
by Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate
Professor, Puyallup Research and Extension Center, Washington State
University

With the exception of arid and coastal regions (where soil salts are
high) and the southeastern United States (where heavy clay soils are
common), gypsum
amendment is just not necessary in non-agricultural areas. Urban
soils are generally amalgamations of subsoils, native and non-native
topsoils, and – in home landscapes – high levels of organic and
non-organic chemical additives. They are also heavily compacted and
layered (and gypsum does not work well on layered soils). In such
landscapes, it is pointless to add yet more chemicals in the form of
gypsum unless you need to increase soil calcium levels. To reduce
compaction and improve aeration in nearly any landscape, application
of an organic mulch is more economically and environmentally sustainable.
http://puyallup.wsu.edu/wp-content/u.../03/gypsum.pdf

What About Gypsum?
By Carl Wilson, Horticulturist with Denver Cooperative Extension
As far as relieving soil compaction, gypsum has no effect. Loosening
soils is a physical process, not a chemical one. The way to break up
tight, clay soils is through adding and mixing in organic amendments.
The amendment holds the clay particles apart creating more space for
the air so critical to plant root growth. It's easy for gardeners
frustrated by hard, clay soils to grasp at anything that sounds like
it might work. With gypsum, the expression "If it sounds too good to
be true, it is too good to be true" applies.
http://www.colostate.edu/Dept/CoopEx...oil/gypsum.htm

Soil Amendments and Practices of Unproven Value
Gypsum (when added to soil to soften clay/loosen compacted soil,
to lower the pH of alkaline soils, to raise the pH of acid soils, or
to treat soil salinity)

Gypsum, which is hydrated calcium sulfate (a low-solubility salt), is
effective in treating sodic soils, which are soils high in
exchangeable sodium. The sodium between soil particles attracts water,
causing the soil to disperse. The dispersed particles seal the soil
surface, reducing infiltration. Addition of gypsum replaces the sodium
on the exchange sites with calcium, which results in flocculation of
the soil particles into soil aggregates. The resultant sodium sulfate
can then be leached out of the soil. Although gypsum does improve
structure in sodic soils, it will not soften clay nor loosen compacted
soil.
http://articles.extension.org/pages/...unproven-value