I get coffee grounds from my local coffee shop. Can I use them directly on the soil as mulch (without mixing anything into it except to rake it into the soil)? The grounds are wet when I get them from the coffee shop. Should I let them dry out a little before putting it on the soil?
In just about every listing of “ingredients” for a successful compost pile, you’ll find coffee grounds among the nitrogen-rich kitchen waste “green” ingredients that make up the mix. But it’s a mistake to use coffee grounds alone. They are very acidic, and over time will change the pH of the soil – the measure of its acidity or alkalinity – to the point that plants that prefer alkaline soil will suffer. Even around plants that prefer acid soil – blueberries, azaleas, rhododendrons – you will likely find that an overabundance of coffee grounds make the soil too acid and will damage the plants.
This information is from gardening expert Mike McGrath, whose gives out garden advice in a radio program, in print and other formats, including the website of the eco-friendly retailer Gardens Alive.
Coffee ground are so rich in nitrogen that you risk creating a “mold bloom” where you spread them “raw.” In addition, the life in grounds alone has been perked away. Create good compost by adding the grounds to yard waste – McGrath suggests four parts shredded leaves to one part grounds by weight.
Other components of good compost can include “green” (nitrogen-rich) items such as fruits, vegetable and fruit peeling and cores, tea bags, egg shells and other kitchen waste, grass clippings, weeds without seeds; and “brown” (carbon-rich) items such as dry leaves, straw and hay, wood chips, newspaper, paper towel tubes, dryer lint, pet hair. Don’t add meat, fish, grease, bones or fat to compost.