Epsom salts add magnesium to the soil in a form that is available to the plants in alkaline soil. It will also lower the pH a small amount. It may not be a good idea to add to a vegetable garden since too much magnesium can be a problem in vegetables (if the plants need it, you can add a little, but be more careful around vegetables).

If your plants have magnesium deficiencies, Epsom salt can help provide the magnesium they need. If you search chlorosis and magnesium, you should be able to find pictures of plants that are suffering magnesium deficiencies. It may be difficult to tell the difference between magnesium deficiencies and iron deficiencies, so try to find information on both.

So Epsom Salt is not SALT - its magnesium? If my soil is magnesium deficient and alkaline and I add Epsom Salt - is that ok?

Im familiar with magnesium/iron deficiencies but (here anyway) the problem lies with the clay soil. Sometimes there are ample amounts of mag/iron but it can't travel to the roots because the soil is so compact. I added and added and added iron to a iron deficient wisteria and it never pulled through because the iron couldnt get to the roots.

As a rule of thumb, it's not good practice to add ANY salt to ANY soil, especially clay. There are, however, exceptions and times when it's OK to bend that rule. Epsom salt MAY be one such case. I say "may" because the jury still seems to be out on whether it should be applied directly to soil. The jury all agree, however, that it is safe and effective (for some plants) when used as a foliar spray. If you think you want to try it, I'd recommend going the foliar route just to be on the safe side.

-Diggity

Here is a link that might be useful: Epsom Salt

Since you discuss both alkalinity and salinity, I'm going to guess that you're in an arid area. These problems are common in arid areas.

If your plants are magnesium deficient, adding Epsom salt should help.

I don't think the problem is with the clay being compacted and keeping the iron and magnesium from getting to the roots. It's more likely that there is plenty of iron and magnesium in the soil, but it's in a format that isn't available to the plants. This is caused by the alkalinity of the soil.

Epsom salt is a salt, but not of the kind that will add to your problems with salinity.

pH problems will often cause certain nutrients to not be available to the plants but be careful of just adding things to the soil because you think there might be a deficiency. You may be better off getting a soil test done before adding much of anything.

Epsom Salts are Magnesium Sulfate, a soluble form of magnesium that is quickly available and then gone. Unless a good, reliable soil test indicates a need for adding Magnesium to your soil is is not a good idea and is seldom really necessary.
The only thing most all soils really need is organic matter. Adding mineral forms of nutrients can, very easily, create more problems than they solve unless that addition is guided by a good, reliable soil test.

From what I'm understanding it's Alkaline in the water and soil, im having problems with a myer lemon tree that is either magnesium or iron deficient I tried the iron and it still kept dropping leaves, so after talking to my neighbor and he tested the water and it's about 8 or higher pH, I live in the high desert of Nevada on the border of California we have poor clay soil and water. So I have decided to try and save the tree with epsom salt I hope it does the trick, I watched my neighbor add vinegar and drop the pH to 7, so im thinking this may work for me.