The directions typically outlined are 1tbsp of aluminum sulfate per gallon of water. I have no idea why sulfate of iron was suggested unless to avoid chlorosis - iron has no impact on flower coloring. It is the concentration of aluminum in the soil that makes hydrangeas blue and the degree of soil aciditythat allows the aluminum to be accessed by the plant. Aluminum sulfate assures both adequate aluminum levels and helps to acidify soils.

I should imagine central NY to have sufficiently acidic soils to make using aluminum sulfate unnecessary.

Thanks. Yeah you would think that in Central NY acidic soil would be a no brainer....not exactly. There is alot of calcium up here. Calcium NY is not too far from here. My soil pH is fairly high......above 7.5 according to the soil test. I'm just getting the hang of this hydrangea thing after almost killing my last one. I'm going to plant another. I think I will wait a year to try any AS on a new plant. I'm definitely going to use some pine bark mulch and a little bit of pelletized sulfer for backfill. Ed

Remember that you have to amend the soil regularly from now on thru "forever" or else your soil will revert back to its original soil pH.

Yes, thanks. I was just checking my soil analysis, and the recommendation is for 36 pounds of Aluminum per acre. Does that mean I have low aluminum? Thanks. Ed. BTW, Zinc is 1.4lbs, Iron is 2.6, and Manganese is 35.8.....everything else was ok.

Oh, gee. This is not a simply answered question :-) First, I'd want to know what type of testing was done as aluminum takes several different forms in the soil, multiple ways of testing and therefore multiple ways to interpret the results. Most soil labs do not test for soluble Al, which is the only form in which the mineral is available to plants. Therefore, without knowing more about the soil testing procedures, it's hard to say wher you are on your Al concentration.

Personally, I'd be reluctant to add more unless I knew specifically that was called for. Aluminum is not an element that is required in any serious concentration by any plant and aluminum toxicity can be a very serious issue to a whole host of plants so I'd use a very light touch. Following the directions for the aluminum sulfate and the hydrangeas is unlikely to create problems for anything else.

I'd be more concerned about lowering my pH. Even with aluminum in sufficient concentrations the soil has to be properly acidic for this element to become available. That's very likely why your soil test indicated adding aluminum - soil is not the slightest bit acidic.

Unfortunately, it takes time to acidify soil and as indicated previously, it is something you will need to repeat regularly. Just a thought, but you may have better success growing the hydrangea in a container (or raised bed) where you can more closely tailor the soil conditions to its needs.

The soil analysis was just a typical test done by the county. FWIW I kind of assumed that the aluminum must be low because of how much was suggested to add.

Well I planted the hydrangea this afternoon. Following the instructions, I dug the hole about twice the size of the root ball, and backfilled with some double ground pine bark mulch mixed with a little of the natural dirt. I mixed in some fertilizer, and about 1/2 cup of garden sulfer. Even though phosphorus is recommended to be on the light side for hydrangeas, I used a little for the root establishment of the new plant. I'm not planning to use any AS until I see how it goes with the color of the blooms, and then sparingly at best. Thanks for all the feedback. Ed