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Using Coffee Grounds Correctly


Question. I don't put much 'green' material in my 12'x7'x4' compost pile; just a lot of coffee grounds. (We drink a LOT of coffee!) Is there a recommended limit? I don't want my plants to OD on nitrogen (or caffeine!).
    ---Ken; just outside of Philadelphia, PA.
I am spreading coffee grounds from the local Bagelsmith under my five-year old pines and spruces with the idea that it will acidify my lousy clay soil. Based on a number of enthusiastic 'testimonials' on a recycling website I have spread several bushels of grounds so far. Am I deluded? Worse, am I doing harm?
    ---Richard at Rutgers University, New Jersey
Mike: I live in a part of the world that's so young geologically it was recently covered with glaciers. There isn't much soil, so I make a lot of compost. Besides the usual stuff (kitchen scraps, newspaper and cardboard), I can receive 30 pounds of grounds a week from the only coffee shop on Prince of Wales Island…
    ---Jay in Craig, Alaska
Answer. First, a few extraneous words to Craig up in Alaska: I know that many uninformed sources advise using shredded newspapers and cardboard as the 'dry browns' in a compost pile, but: 1) newspaper ink is more toxic than these people realize; 2) newsprint is bleached, creating cancer-causing dioxins; and 3) cardboard contains nasty glues and other chemical 'fillers'. More importantly, these things contain zero nutrition for your plants. If you don't have enough leaves, experiment with wood shavings or sawdust. They can be difficult to compost, but are far superior to heavily processed paper products.

Now, on to coffee grounds! When we first started doing this show, we warned people to only spread coffee grounds around acid-loving plants, like azaleas, rhododendrons and blueberries, because the grounds were bound to be acidic; and not to overdo it on those and other flowering plants, as the grounds were certainly high in Nitrogen, which makes plants grow big, but can inhibit the numbers of flowers and fruits.

But then we were sent some test results that showed grounds to be neutral on the pH scale! To find out what gives, I called Will Brinton, founder and Director of the Wood's End Research Laboratory in Maine, the definitive testers of soils, composts, and raw ingredients used in large-scale composting. Will solved the mystery instantly. Woods End, it turned out, was the source of that neutral test! Ah, but some follow-up investigation later revealed that it hadn't been coffee grounds alone, as the person submitting the material for testing had stated, but grounds mixed with raw yard waste, the classic 'dry brown' material that is the heart of a good compost pile.

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