Garden Fundamentals
21 minutes
Aluminum Sulfate Lowers Soil pH Within Weeks but Risks Aluminum Toxicity
Aluminum sulfate acidifies on contact but needs ~6 times the weight of elemental sulfur for the same pH drop, and the Al³⁺ it adds injures roots below about pH 5. A drench of about 1 tbsp per gallon turns hydrangeas blue; avoid it in vegetable and blueberry beds.