Coffee Grounds in Compost Bin, Composting, Making Compost: Gardener's Supply

by Kathy LaLiberte

When I go to my local coffee shop, I often come out with more than a cup of coffee. Near the door, they have a bin with free bags of used coffee grounds. Like most avid gardeners, I find it impossible to resist free food for my garden!

In the spring, I spread handfuls of coffee grounds around my acid-loving plants—azaleas, blueberries, rhododendrons. The grounds are slightly acidic and besides helping to lower the soil pH, they foster the humus-rich soil texture these plants really love.

In late summer and fall, I dig coffee grounds right into the vegetable garden after removing early-season crops such as peas and spinach. In the winter, I add the grounds to my compost pile. They’re a good source of nitrogen at a time of year when that can be a little difficult to come by.

Here’s a quick refresher about how to build a good compost pile by combining “green” ingredients such as coffee grounds, with “brown” ingredients such as dry leaves.

Browns & Greens
Efficient composting depends upon a well-balanced mix of ingredients, which generally fall into two categories: browns (high carbon), and greens (high nitrogen). The ideal ratio is 25:1 (brown to green) but most people find three parts brown and one part green works quite well. Remember to layer your ingredients, keep the pile moist (like a well-wrung sponge) and turn it occasionally to incorporate a fresh supply of oxygen for the microbes.

Here's a list of some common compost ingredients in each category:

Brown (3 parts)

corncobs and cornstalks

paper

pine needles

dry leaves

sawdust or wood shavings

straw

woody vegetable stalks

Green (1 part)

coffee grounds

eggshells

fruit trimmings

vegetable peels and leaves

grass clippings

feathers or hair

green leaves

seaweed

fresh weeds

rotted manure

alfalfa meal

More Information
Master Composter, a web site for composting enthusiasts, conducted a Coffee Grounds Survey on the use of grounds--in compost and in the garden.
If you're looking for a source of grounds, try Starbucks Coffee and Peet's Coffee. Both companies have researched the issue further and share the results on their web sites.