Coffee that has been roasted but never brewed is fine for acid-loving plants, including rhododendrons, azaleas, hydrangeas, Pieris, andromeda and camellia. Uyterhoeven suggests sprinkling those grounds in a thin layer around a bed of acid-loving plants, along with a layer of mulch.

Trick is to get 30% acidity vinegar solution. He uses combination of 30% vinegar, salt and dishsoap.