Using Coffee Grounds in the Garden
July 16, 2013
There seems to be a lot of confusion about using spent coffee grounds in the garden. You can use coffee grounds directly in the garden, but as with anything, moderation is key.
It's often stated that coffee grounds are acidic, and therefore good for acid loving plants like hydrangea and azalea. However, as coffee grounds decompose in the soil their acidity neutralizes...so the soil acidifying effects are minimal and short-lived. You'll see recommendations to add fresh spent coffee grounds directly to the soil around the plants. But how much? Typically, you never want to add more than about an inch worth of coffee grounds around base of the plant, to the drip line. Then gently work it into the top layer of the soil. Make sure these original coffee grounds are completely decomposed before you add any new grounds. Roses, hydrangeas, hollies, and azaleas are all good candidates for coffee ground amending, but you can use them for any plants in your garden.
So what do coffee grounds do exactly? Well, they are a source of Nitrogen. However, that doesn't mean that coffee grounds are an instant Nitrogen fertilizer. Rather, as they decompose and are broken down by microbes, Nitrogen will be released and available to plants. So it takes time. You should think of coffee grounds as more of a soil amendment, like compost, rather than a fertilizer.
Where coffee grounds really go to work is in the compost bin. If you've used the maximum recommended amount around your plants already, the leftovers should go into the compost. If you're not sure how to make compost, all you really need to do is balance your "greens" and "browns". The "greens" are your sources of Nitrogen. The "browns" are your sources of Carbon. So which category does coffee grounds fall into? GREEN! That's right; because it's a source of Nitrogen, you should consider coffee grounds a "green", even though they are brown. Other greens would be vegetable kitchen scraps, fresh green pulled weeks or fresh green grass clippings. Browns are made up of dried leaves, dried grass clippings, newspaper, wood ash, etc. To properly balance your compost, just mix a ratio of 1:3 of greens to browns, by volume. So for 1 bucket of "greens" add 3 buckets of "browns" to balance out the compost. This will ensure a proper balance of nutrient sources for the beneficial microbes that will break down the compost. Make sure your compost gets about a half day of direct sun and you keep it moist, about the consistency of a wrung out sponge. Turn your compost regularly to aerate it.
Now, go drink your coffee and stop throwing those grounds in the garbage can!