Most people who think about composting think about their yard waste and maybe some kitchen scraps. Few think of coffee leftovers as compost material. Coffee grounds are an excellent addition to the compost heap. If the filters used are natural fiber, biodegradable filters (most are paper or cotton), they can also be included in the compost. Many leave the grounds in the filter and throw the whole shebang into their compost bucket or pile. An easy, clean solution that can save many pounds of landfill waste annually.
Benefit of Coffee Grounds to the Soil
The high nitrogen content of the grounds is the largest benefit to the compost and soil. Many people ordinarily would use nitrogen-rich chicken or bat manure as their primary nitrogen source for their compost. The trouble is, if you don’t know where the manure is coming from, exactly, or what’s been fed to the animals from which it came, that manure could have pathogens or other issues. With coffee grounds, those problems are nonexistent.
After brewing, coffee grounds go from being acidic to becoming nearly pH neutral (usually 6.5-6.8). This is because the acid is imparted to the coffee, giving it its characteristic bitter taste. Cottage industries around coffee shops have sprung up with master composters creating and selling coffee grounds-based compost for nitrogen enrichment for home gardeners.
Composting Coffee Grounds
There are two primary means of utilizing coffee grounds as compost. In both cases, the grounds must be given a chance to compost, since they are at about a 20:1 ratio of carbon to nitrogen when fresh out of the pot. If needed, grounds can be saved in buckets or other air tight containers until needed and the mold that’s produced will die off when exposed to dry air or the heat of a compost pile.
The first is simply to add it as a soil amendment directly, spreading them on the ground and covering them with a light mulch. This is especially popular in the fall and winter after harvest, in order to allow the coffee to percolate, as it were, into the soil. It can also be done in the early spring, two or three weeks before planting.
In a regular compost pile, grounds can be added, filter and all, to an unturned pile at up to 25% of the pile’s total volume. Grounds, because of their easily released nitrogen content, will cause the bacterial reactions in the compost that create heat and beneficial gasses. So at a 1:4 ratio, the heap will warm up considerably and maintain a 135 degrees Fahrenheit or better core for a relatively long period. This will kill most of the weed seeds, grubs, and pathogens that could be lurking in the compost.
Otherwise, treat your compost normally. Turn it about once a week or so and mix in your coffee with at least three times as much carbon material (grass, leaves, etc.) with each addition.
Vermicomposting With Coffee Grounds
Worms love coffee, probably for reasons similar to our own. Coffee is related to the cocoa bean and contains many of the same nutrients, most of which are not leached away to the brew you’re drinking. So those nutrients are retained in the grounds, for the most part, and your worms will love them.
For vermicomposting, add as above. Be sure to include at least an equal or 150% part vegetable matter to go with the grounds. Some have said that if you give your worms coffee grounds, when you open the bin and listen carefully, you’ll hear them chanting your name with joy. The late night worms will especially love you for the coffee.