Coffee compost

Q.  I drink a lot of coffee. A. Lot. And I’m just getting into composting, so I’m tempted to try using all the grounds in my garden as fertilizer. But will the grounds be too acidic? – Sarah, NH

A.  Sarah – define “a lot.” If you’re going through five industrial-sized pots per day, the amount of used coffee grounds you sprinkle on your garden is frankly the least of your worries. If not, sure, definitely go ahead and use your grounds as a fantastic, free, natural fertilizer. (And if you ever have cold, leftover coffee in the pot, go ahead and pour that directly onto your garden or lawn, too.) You’re right that grounds can be a teensy bit acidic (though used grounds are far less acidic than raw grounds), so they’re great for clay-based alkaline soils. Or sprinkle the grounds over acid-loving plants (which like a low pH of around 4 or 5) like azaleas, rhododendrons, potatoes, and blueberries. If your soil is on the more acidic side, and you’re not interested in growing any acid-loving plants, just temper the acidity of your grounds by throwing them in the compost heap instead of directly on your garden.

And guess what else? Coffee grounds are… wait for it… a natural slug repellent, so they’re a rich fertilizer and effective pesticide in one. Without all the chemicals.

For those out there who don’t drink coffee, but want to fertilize naturally and save money:  Ask the barista at your local coffee shop for some leftover grounds. Or maybe you work with a bunch of caffeine junkies? Collect grounds from the kitchen at work and bring them home. And if you’re still struggling with the idea that coffee grounds make excellent fertilizer, check out this LA Times piece on Mike Theuer, who sold his little coffee shop in PA because he realized he could do better selling coffee fertilizer than he could selling coffee. He cuts acidity by adding a bit of limestone to his formulas—browse his products online at Grow Joe.

-  Tobin Hack

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