Your morning cup of coffee can do a second job in the garden. Used coffee grounds are free, easy to collect and full of organic matter, and gardeners have found plenty of ways to put them to work. They’re most useful when handled the right way, in moderation, and either added to compost or spread in a very thin layer. Here are five easy ways to make the most of them, along with the mistakes to avoid.
Add them to your compost
This is the simplest and safest way to use coffee grounds. They count as a “green” ingredient, like grass clippings, adding nitrogen to your compost pile. Mix them with dry “brown” material such as fallen leaves, and keep them to no more than about 20% of the pile’s volume. A handy recipe is three parts leaves to one part fresh grass clippings to one part coffee grounds. Paper coffee filters can go in too. After a few months, you’ll have dark, crumbly compost for your beds.
Use a thin mulch layer
Coffee grounds can help as mulch, but only if you keep the layer thin. Half an inch is plenty, topped with about four inches of a coarser material such as wood chips. A thick layer of grounds on its own can pack down into a crust that blocks air and repels water once it dries. Spread them around established shrubs and perennials, and avoid piling them against plant stems.
Feed your worm bin
If you keep a worm bin, coffee grounds make a welcome treat. Worms happily eat them, and the finished vermicompost is a rich, gentle soil booster. Add the grounds in moderation and mix them with other kitchen scraps and bedding, since too much of any one thing can upset the balance. If you don’t have a worm bin, mixing a little into outdoor garden soil also adds organic matter, as long as you give your plants a source of nitrogen too.
Try them against slugs and snails
Many gardeners sprinkle a ring of used coffee grounds around plants that slugs love, such as hostas and lettuces. Results vary, so think of it as one part of a wider approach rather than a guaranteed barrier. A thin, dry ring works best. Keep it narrow so it doesn’t clump, and refresh it after rain.
Know the myths and mistakes
A few common beliefs are worth correcting. Used grounds aren’t very acidic, with a pH of about 6.5 to 6.8, so they won’t reliably acidify the soil for blueberries or hydrangeas. They also contain only about 1 to 2% nitrogen, so they’re a soil conditioner, not a fertiliser. Fresh, unbrewed grounds are more acidic and contain more caffeine, which can hold back growth, so stick to used ones. And never leave a thick, wet layer, which can turn mouldy.
Disclaimer:
This article is intended for general gardening guidance only. Results vary with soil, climate and the plants you grow. Use only used, cooled coffee grounds in small amounts, keep them away from pets (caffeine can be harmful if eaten), and consult a local nursery or extension service for advice specific to your plants.
