Epsom salts

[dannysmom]

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.

[told2b]

Epsom salts contain two elements magnesium and sulfur. It's considered a neutral salt, having little effect on soil pH. If your soil is acidic add dolomite lime, it wil add magnesium while raising the soil pH. HTH

[JohnS]

Sulfur to alkaline soil and limestone for acid. Are you planing something with special needs as to PH?

[David E. Ross]

Being a sulfate, Epsom salts (magnesium sulfate) are somewhat acidic. Unless you specifically want to add magnesium, however, I would not use Epsom salts to adjust the pH.

To reduce the pH, add elemental sulfur to the soil. Granular or powdered soil sulfur is available at low cost in most nurseries. Bacteria in the soil convert the sulfur into sulfuric acid.

To increase pH, add lime to the soil.

You want to add Epsom salts when perennials and shrubs fail to produce new shoots from the base. Today, I divided about a 1/4 cup of Epsom salts around seven rose bushes to promote new canes for this year's growing season. I then added another tablespoon to one rose that has only a single cane (the result of an accident that broke down the bush last summer). Magnesium will help the roses create new canes from the bud union.

[hairyarms]

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

[David E. Ross]

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.

[dannysmom]

Thanks everyone, for the helpful replies. I'm sure what I have is a cheap tester, so I won't rely on the results. I think I'll play around with it on my houseplants.

I was hoping to use it to help me turn my hydrangeas blue, as the blooms thus far have been beigey -pink.

The advice for using epsom salts on roses is great. Thanks

[Jangchub]

I didn't read all the replies, but if you put sulfur at the base of your hydrangea it may or may not help with blueing the flowers. Some varieties are always pink or white or beige. Do you know what kind of hydrangea you have?

[dannysmom]

It's supposed to be a Nikko Blue. If I apply the sulfur this spring can I expect blue blooms this summer?

[Hal]

Use the following to determine final bloom color (determination of bloom color is set approx. late Aug-early Sept.):

pH >7.0 = red

6.5 - 7.0 = white 5.5 - 6.5 = pink 4.5 - 5.5 = blue