Ammonium sulfate will help acidify your soil, which will make any aluminum ions already in the soil more available to the hydrangeas, and so, technically, ammonium sulfate will help turn hydrangeas blue. But, adding the aluminum and acidifying at the same time by using aluminum sulfate gives the double whammy, and more assures the blue color. As for AlSO4 sources, have you gone to Home Depot and Lowes? I bought it at HD last year. - Steve

The instructions vary with the type of ammendment used. You shouldd try to add the "proper" amount three times a year while the plant is growing and the ground has not frozen. Say, May, June, July. If you are located in the southern states, you could apply once more. For example, Espoma sells Organic Sulphur which is 90% sulphur and they suggest 1/4 cup for new plants and 1/2 or so for older ones. Other packages by other vendors do not even say, which drives me up the wall!! The correct way to do this requires that you know (a) what is your current Ph Level, (b) what Ph Level you want to do down to and (c) what type of soil do you have (clay, sandy, etc). Luis

I set up an experiment with Nikko blue big(3ft.) bushes. some treated with aluminum sulfate, some controls not touched, and others treated with an organic acidifier from Pettitti's garden store in Strongsville, Ohio.The untreated controls and organic treated are PINK. The AS treated are lavender/purple. I will reapply AS three ounces around drip perimiter of those plants, and water in well to try to get real blue as I fell in love with in Massachusetts everywhere.and keep blogging. MF Medina, Ohio-- former OSU master gardener and retired Cleveland Public high school teacher.

Good morning, mercime. Aluminum sulfate comes in several forms (powder, etc) and in several concentrations so a single formula will not work for all versions sold out there. I hate it when they give me weight requirements like that (because I have no scales of any type) so, what I do is determine how many pounds I will need as a percentage of the package's weight and take out that much. So if I need to apply 1 pound and the package weighs 4 pounds, I extract 1/4 of the package's content. Because less is more when dealing with compounds that have Sulphur, feel free to use less anytime. Because my soil contains naturally occuring aluminum but is alkaline, I always have to apply something in Spring and sometimes again in the Fall. My bag of a/s is now empty since last Fall and I am just using Garden Sulphur. If your soil has adequate amounts of aluminum, you can do the same; otherwise stick with a/s. You can also use iron-chelated compounds or greensand if you are into organic stuff.