Jack Stooks, who worked at Highgrove House for more than two decades, told Coffee Friend that used coffee grounds can be great for helping the acid-loving plants thrive. He said the key to unlocking the benefits of coffee, as well as the common mistakes you’ll want to avoid.
Jack said: “Coffee grounds tend to work best on acid-loving plants, so think rhododendrons or azaleas. Coffee contains nutrients like nitrogen, potassium and magnesium, which help plants grow strong and flower well. As the coffee grounds break down, they also improve the soil and help it hold onto moisture.”
“Ideally, dry your coffee grounds out first. I usually spread them out on a baking tray on sunny days and then store them in an airtight container. When you’re ready to use them as a feed, mix the dried coffee grounds with compost before applying them around the roots of the plant. Lightly work the mixture into the soil and water it in well.
“Using wet coffee grounds can lead to mould, which is something you want to avoid. Mixing the grounds deep into compost also helps incorporate them more evenly into the soil and prevents pets, particularly dogs, from eating large clumps, as coffee can be toxic to them.”
Deter pests but not pollinators
“Dried coffee grounds can also help deter slugs and snails. For plants like delphiniums or hostas, try placing a ring of dried coffee grounds around the base of the plant. Slugs and snails are less likely to cross it because of the rough texture, while the caffeine content can also act as a deterrent.
“It won’t stop every pest, but it can help reduce damage and discourage them from ruining your plants. I wouldn’t recommend using coffee as a spray on plants, though, as it can also affect pollinators, and protecting pollinators is really important for a healthy garden. Instead, test dried coffee grounds in small areas first and see what difference they make.
“It’s also important not to overfeed the soil with coffee grounds, as too much can make it overly acidic. Use them gradually and think of coffee grounds primarily as a plant feed, rather than simply a way to get rid of pests.”