You probably should get a compete soil test first. Some soils are too high in magnesium (and some limestone contains plenty of magnesium). I don't know if high Mg problem soils occur in Illinois. Also a small experiment done at Auburn showed that very high doses of epsom salt (as recommended by that trade association) reduced bloom of roses. The various cation nutrients can compete with each other, so you don't want a gross imbalance of any. I wouldn't use it unless you know there is a deficiency.

Soils in my neighborhood are low in magnesium, and I sometimes see the distinctive deficiency pattern on various roadside plants. I also see it in my garden on balloon flower and my WS2000 rose. Therefore, I throw a little epsom salt on that bed once or twice a year.

Possibly somebody just made up the stuff about strengthening cell walls. Magnesium is used primarily in the chlorophyll molecule. It also occurs in the red pigment anthocyanin, but I saw a study where epsom salts did not affect color in red tuberoses (which of course are not roses). Remember that many red roses change color week-to-week depending on the weather.

I was confused, so I found some info:

Dolomite limestone contains 8 to 20% Magnesium, versus epsom salt of 10%. Limestone is calcium carbonate, zero magnesium.

Formula for dolomite limestone is CaCO3 + MgCO3. Formula for limestone is plain calcium carbonate, CaCO3.

Dolomite limestone is grayish-whitish in color, limestone is most often yellowish. The Great Pyramid in Egypt is made out of limestone. I dug out tons of yellowish limestone in my soil, and there's a limestone quarry nearby, our hard water is high in calcium, zero magnesium. I copied the below info. to clear up the confusion:

There are a number of limestone mines throughout the world, but in particular in the United States, within the midwest and in the west. The primary difference between Dolomite and Limestone is that true Dolomite contains both Calcium and Magnesium whereas Limestone is primarily Calcium Carbonate.

Lack of nitrogen shows first in older leaves, whereas iron deficiency shows first in newer leaves.

Iron deficiency is indicated by a yellowing that begins in newer leaves. The internal veins in the leaves are often still green. Iron deficiency can also be caused by overwatering. Magnesium deficiency causes older leaves to yellow at the tips and then die back. It can look very similar to salt burn but can be distinguished from salt burn by the fact that it concentrates itself on older leaves and affects the leaf tip rather than traveling the margins of the leaves. This is shown best in tomato plants.

My neighbor planted his maple on a pile of limestones, versus mine on 10 bags of topsoil. His leaves are yellow, with deep green veins. Mine are normal green. I have just plucked a few leaves from his tree. Conclusion: they best match magnesium deficiency pictures. Magnesium deficiency occurs mostly in sandy soil, but it can also occur in high alkaline limestone soil.

Strawberryhill, you might find the linked article, by Dr. Lindea Chalker-Scott of Washington State University on epsom salts as a garden Myth, to be interesting reading. Dr. Chalker-Scott takes a hard line on any miracle garden treatment that lacks sound evidence.

Here is a link that might be useful: Epsom Salts

The Mill's Magic Liquid Feed contains magnisium sulfate but Mill's Magic Rose Mix does not.
You should invest in a good soil test before using soil amendments to make sure you're not adding to a problem.

Thanks for the info. (I read the whole thing). I am confused by this article from Cornell University Extension, recommending epsom salt for crops: http://nmsp.cals.cornell.edu/publications/factsheets/factsheet59.pdf

Conclusion: The best way is to remove those darn limestones, rather than adding leaking epsom salt. The maple leaves I picked from my neighbor's tree also match manganese deficient maple leaves grown on alkaline, high calcium soil.

New York folks are pretty big on epsom salt (as seen by New York rose society' recommending epsom salt after 1st frost for roses' hardiness). That article from Cornell University about magnesium deficiency in NY must has something to do with it.

I use epsom salt in early spring when they break dormancy and maybe some at the end of July. My understanding was that it promoted basal growth. I can't say if it does or not. I do get new basal breaks in the spring but then I probably would anyway. I can't say that I've ever noticed any great onslaught of new basals in August when I've used it in July.

Glad to hear from you, Seil, the lady with many roses (I'm in love with your pics posted in the rose gallery).

Karl, I did check my County Extension Service on soil test, it's $20 for basic NPK (which I already did myself with $12 kit from Lowe's) - and $30 for sulfur, manganese, iron, boron, but NO magnesium test.

I already know what's wrong with my soil: those blasted limestones. Remove them, and my plants are healthy. I did check past soil forums: someone with sandy soil did a soil test and was surprised to see high magnesium !

A balance of calcium and magnesium is essential in the human body, but plants? Cornell University thinks we need it for crops. We get magnesium in terms of spinach and greens for the human body, so I think organic matter solve the problem just as well as epsom salt - unless my roses are severely constipated, I might try epsom salt. Ha! Ha!

Magnesium deficiency on rose does show chlorosis around the margins and between the veins, but leaving a green area alongside the veins. Also it starts at the bottom of the plant and progresses upward gradually.

Here is a link that might be useful: pic of Mg deficiency

Thank you, Michaelg, for that tip. What would us newbies do without you? I appreciate all the help you have given, we all are lucky to have you in this forum.

I read your link, and went out to check my Dogwood tree. The yellowish leaves & green veins are most at the bottom of the tree. My picked leaf matches with the picture in the link. The magnesium deficiency shows more with acid-loving trees, such as red maple and dogwood.

I'm a bit curious about Roses Unlimited's recommendation of 1 cup Dolomitic Lime (20% magnesium) in the planting hole. Their website shows picture of William S. rose with the most vibrant red color. Heirloom Roses also recommends epsom salt to deepen petals' color. I am curious as to what Pat of RU says about magnesium and her deep red Shakespeare. Next April I'll ask her.

I find Mike's link to be useful, about epsom is ONLY best used in high-crop production, such as tomatoes on old soil: Here's a paragraph from Mike's link:

"Excessive levels of potassium contribute to a mineral imbalance that causes magnesium deficiency in a variety of species, even when soil levels of Mg are adequate. High levels of soil potassium apparently interfere with root uptake of recommended to overcome this indirect magnesium deficiency; trees high in nitrogen were found to be less susceptible to magnesium deficiency than those with reduced nitrogen levels."

My clay soil tested very high in potassium, next is phosphorus, and least is nitrogen. Plants short on potassium are more prone to fungal diseases. I have zero blackspots on roses, but have problems with magnesium deficiency esp. in my tomatoes, grown in the same bed for 12 years.

Fifteen years ago my other garden had a different soil: no clay, just good black dirt high in nitrogen. We never had to fertilize the lawn, everything was green, but I had the worse blackspot on my roses.

I have never used epsom salt on my tomato, but last year when I mixed bagged cow manure in, we had a bumper crop of tomato. This year I didn't do that, and we have the worse crop of tomato and very small fruits. I'll do an experiment next year growing tomatoes in 2 different pots, water one with epsom salt, and let's see if the fruits get bigger.

There are a few You-tube on experiments with tomatoes with epsom salt. But I'll do my experiment on alkaline clayish limestone soil, rather than potting soil.

Here is a link that might be useful: You tube on tomato & epsom salt

Epsom salts should not be applied to soils unless a reliable soil test says otherwise...

I'm still looking for a calcium/magnesium test in Illinois (just to double-check with my well water report of high calcium, zero magnesium). If I don't find one, I won't waste my time using epsom salt.

This summer I did 3 pots of geraniums: 1) 100% Miracle-Gro potting soil 2) potting soil on top, half yellowish clay at the bottom 3) potting soil on top, half soil/horse manure at the bottom

Here's from last August to now result: I like the look of pot with yellow clay at the bottom the most: geranium leaves are yellowish, green veins with bright red tinge at edge (like early fall color). I am getting to like this magnesium-deficiency look, so why change?

For folks in Michigan, here's a reliable source for soil test: Posted by kimmsr 4a/5b-MI (My Page) on Tue, Jul 6, 10 at 7:03

A very good and reliable soil test, soil pH, Phosphorus, Potash, Calcium, Magnesium, and soil CEC, from Michigan State University costs $15.00. A major advantage is that you get the level of Calcium and Magnesium which helps determine why your soils pH is where it is. Your pH meter will not supply that information.

I got into Karl's recommended website again (somehow I didn't find the info. the first time). Will order that test from Karl's recommended site.