Posted by wendyb 5A/MA (My Page) on Tue, Jul 14, 09 at 15:05

thinman, while we're on the subject, seems like you may know the answer to this. I keep getting these mixed up. Which is best for my hydrangeas and which for my blueberries?

ammonium sulfate

aluminum sulfate

garden sulfur

Posted by morz8 Z8 Wa coast (My Page) on Wed, Jul 15, 09 at 0:27

Wendy, Never use aluminum sulfate to increase soil acidity (or lower the ph) as it can be toxic to many plants including your blueberry. Aluminum sulfate is soluble in water thus the aluminum component is immediately available in amounts that can kill them. Ammonium sulfate or garden sulfur would be better choices for lowering soil ph (make it more acidic) but you need to know your approximate natural ph before attempting to change it...have a goal in mind. Does the blueberry look chlorotic where it may be in soil too alkaline? As for the hydrangea, using garden sulfur would increase your chances of blue over the pink it would be in more alkaline soil.

Posted by thinman Z5 MI (My Page) on Wed, Jul 15, 09 at 13:22

Wendy asked Which is best for my hydrangeas and which for my blueberries?

ammonium sulfate

aluminum sulfate

garden sulfur

Wendy, I know some chemistry, but I'm not a soil chemist, so believe me when I say I'm no expert. I know that sulfur works, but is slow-acting. Aluminum sulfate works and is very fast acting. It's true that dissolved aluminum is toxic to plants in high enough doses, but it's also true that the dissolved aluminum reacts with soil water to form aluminum hydroxide, which dissolves very poorly, tying up most of the aluminum.

If you follow the application rates on the package, are you likely to kill your plants with aluminum? I dunno, but it seems unlikely, or wouldn't there be a lot of dead plants and unhappy customers out there? Lowering the pH way too much can increase the amount of dissolved aluminum in the soil to the point of killing plants, so I think Morz8 gave you good advice about knowing what pH you already have, and having a pH goal in mind so you know when to quit.

Ammonium sulfate certainly works too, and the short answer to your question is probably that there is no best choice. They all work.

ThinMan