Expert: Long Island Gardener - 5/24/2006

Question
I have a friend who works at Starbucks who says she can give me their coffee grounds at the end of the day.  We have a decent garden, but I was wondering what I can do with these since they are free and it s probably are going to be  raining coffee grounds  all summer for us.  How can I take advantage of this opportunity, if any?

Answer
Here it is, the Coffee-Lover's Guide to Gardening.

Coffee is an acidic soil conditioner, as any coffeelover who has ever had Ulcers or Heartburn can tell you.  One tester clocked a cup of Starbucks at 6.3.  But coffee grounds have a relatively neutral pH of around 6.7.  A neutral pH is 7; acid is anything below that.  

Plants that thrive in acid soils (Annuals and otherwise) will love your coffee grounds.  But they will like leftover coffee even more!  

Hydrangea blooms will be Bluer than ever.  Roses and Tomatoes prefer a slightly acid pH of 6.5-6.8.  Sprinkle the grounds as mulch around Azaleas and Rhododendrons, Blueberries, Magnolias, Ferns, Lupines, Lilies, Irises, Gardenias, Wintergreen, Garlic and Citrus plants.   Your lawn and most flowering plants however will prefer Alkaline soils.  For them, stick with a liberal amount of Grounds and skip the cup of Coffee.

Coffee (black) and Grounds (which has an N-P-K ration of 2-0.3-0.2) are very high in Nitrogen and other nutrients.   Plus latest research also finds Coffee Grounds not only attracts earthworms, but also repels slugs!

Alaska garden editor and photographer Marion Owen writes that USDA scientist Robert Hollingsworth and colleagues were doing field testing of caffeine sprays when they found a 1-2% caffeine solution killed nearly all slugs and snails within two days.  Conclusion: A black cup of coffee is not only effective as a slug repellent; it is even better than coffee grounds.

Owen notes, in fact, the black coffee works better than the Snail Bait you buy off the shelf containing metaldehyde, which is poisonous to pets and wildlife.  An MSNBC reporter recently measured 40 mg of caffeine per 100 grams of freshbrewed Starbucks.

Gardeners who are not fortunate enough to have friends who work at Starbucks can visit the Starbucks Web site.  

I also recommend www.garden.org, "Grounds for Gardens Perk Up Your Plants" and the Garden Plant Care website www.gardenplantcare.com "Perfect Soil for Growing Great Tomatoes".