What is the best way to safely acidify soil where I already have plants?
Applying elemental sulfur is the best way. Sulfur is very slow acting (it may take as long as 3-4 months to be effective). Applied at recommended rates, it’s safe for your plants. Iron sulfate it good, too. Iron sulfate acts more quickly (it takes about 2-3 weeks to affect the pH) but it takes a lot more of the chemical compared to using elemental sulfur. Be especially careful with iron sulfate. It will leave rusty stains on your clothes, sidewalks and patios. It’s even a good idea to wash your gardening clothes separately from your other laundry after spreading iron sulfate. Is aluminum sulfate an option? It is sometimes recommended as a method of lowering the pH enough to turn Nikko Blue hydrangea blooms from pink (bloom color when the soil is alkaline) to blue (indicating the soil is acid enough), but it should not be used on a regular basis. The heavy metals will accumulate and become toxic to the roots of plants. Is there anything else that will acidify as quickly without the draw
