Hydrangea Blue Alum

Blue hydrangeas remain blue in (very) acidic soil. To quickly change the pH of the soil, the fastest way is to administer potassium alum. Apply in small portions to prevent burning. Annual dosage 20-100 grams per plant, depending on age and size. Never apply more than 20 grams at a time. Do not apply during dry and hot weather; alum is usually applied in spring and autumn.

Names:
Also known as: Aluminum sulfate