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David E. Ross · 06-03-2007, 03:48 AM posted to rec.gardens

wrote:
On Mar 5, 3:15 am, "dannysmom" wrote:
Do Epsom salts affect soil ph? I was given a soil ph tester as a gift
and am wondering what to use to adjust soil ph as needed. Thanks.

Epsom salts is Magnesium Sulphate. Its solution is roughly neutral as
it is the salt of a strong acid and a strong base. In the sort of
quantities that you are likely to add to soil it will have no effect
on pH at all. As a soil additive it is used in small quantities as a
quick fix to supply soluble Magnesium to plants with that deficiency,
there is no other reason I can think of to use it as a soil additive.

Garden lime (calcium carbonate) and dolomite (magnesium/calcium
carbonate) both raise pH but be aware that it will take weeks to years
to have a significant effect depending on the nature of your soil, its
current pH and how much you need to raise it. Raising pH is often
required as many soils are naturally too acid for the plants we like
in our gardens and because compost and rotted vegetation is slightly
acidic and if added to soil regularly it will slowly lower the pH over
a period of time.

Lowering pH is not done so often except (for example) if your district
is an alkali basin or has lots of limestone (calcium carbonate)
around. Sulphur can be used but this will be dfficult and expensive
in large areas and you may be better off just growing plants that like
the pH that you have or importing some good topsoil.

Cheap probe type pH testers (if that's what you have) are often
unreliable. If yours tells you that your soils pH is way off I would
cross check with a dye indicator test kit before spending much time
and effort trying to amend soil that possibly isn't so bad, Indicator
kits are quite reliable within the accuracy required by the home
gardener and quite cheap.

David

In much of southern California, the soils are alkaline. I rarely see
lime or dolomite in the nurseries here, but they all carry soil sulfur.

--
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 pages at http://www.rossde.com/garden/