Hydrangea colours
Can I use tea bags and coffee grounds to keep my hydrangeas blue?
Both coffee grounds and tea leaves are very mildly acidic, so adding them to the soil may help acidify the soil and promote blue flowers. You could apply them as a (cold) mulch around the base of your plant. The amount you need will depend on the natural acidity of the soil and the hydrangea cultivar. You’re unlikely to overdo it, unless you run a tea shop! A more predictable way to produce blue hydrangeas is with a plant enhancement salt (such as J Arthur Bower’s hydrangea colourant , £1.99 for 500g). This contains aluminium sulphate, which is the soil nutrient responsible for enhancing the blue pigment.