Q. I recently discovered several unused tins of coffee—some open, some still sealed—that have been sitting in my (dry) cupboard for years. Can they be used on plants and shrubs? (Specifically: camellias, evergreens, hostas, day lilies, black-eyed Susan and garden pinks.) I know you typically advise adding such things to a compost pile; but would the coffee harm those plants if I just spread it around them? I don't have a compost pile. In fact, I'm a very senior citizen with limited ability to garden (I pay others to cut my grass, pull weeds and such), but I still love your program—even if I can't do many of the things you advise. Thanks,
- ---Sylvia in Pennsville; Salem County, NJ
You are correct that I have, in the past, focused on incorporating coffee grounds into compost piles. That's because coffee grounds can be very acidic, and I'm concerned that people will use them on inappropriate plants and make the soil more acid than those plants like. Coffee grounds are also very high in nitrogen; making them an iffy amendment for flowering plants, as too much nitrogen will make plants grow abnormally large, but inhibit the number of blooms. (As in the classic twenty-foot high tomato plant that produces two tomatoes.)
But coffee grounds have few potential negatives in a compost pile, where they are a great high-nitrogen component for mixing with shredded fall leaves. Five to ten pounds of spent grounds mixed into four cubic feet of shredded leaves will create very high quality compost in a very short period of time; it's just an ideal combination. And I expect that your old, un-brewed coffee would act just like grounds in a compost environment.
But I understand that's not an option in your case—heck, you are to be commended for still gardening! AND I've been experimenting with straight grounds myself lately. After my azaleas flowered this year, I thought that a couple of high-nitrogen feedings might perk up the never-fed plants, while also insuring that their soil has the high acidity they famously crave. And I figured they wouldn't be setting next year's buds until mid-summer or so, by which time the nitrogen—a plant nutrient that is famously short-lived and ephemeral in the environment—should no longer inhibit any flowering.
So far; so good. Their very deep green leaf color reveals that the plants really enjoyed their caffeine jolt. Of course, I won't know about the flowering part until next year—but I remain cautiously expectant of a stellar show.
So I grant you an unconditional 'yes' on distributing some of that ancient coffee around your acid loving azaleas and camellias. Let's say up to a pound or so of coffee per plant. You could also give some to your evergreens, but I generally don't recommend feeding those kinds of plants. I have never fed my evergreens; and they thrive.
My biggest personal use of straight coffee grounds has been to apologize to five blueberry bushes whose life with me has been so rocky the Red Cross came by to ask if the plants needed blankets or lawyers.
When I first got them, I acidified their soil heavily with peat moss, which they liked; and covered that with compost, which they liked. But I also lazily planted them in an area with "limited sun" (translation: stygian darkness), which they did not like. So I moved them to a sunnier spot, mulched them heavily with peat moss and covered the peat moss with one of several bagged high-end composts from Maryland I was testing. The plants turned yellow, dropped all their leaves and the Red Cross returned to notify me of imminent UN sanctions.
A more careful reading of the bag revealed that the specialty compost I had used was designed for feeding a lawn, and contained added lime to neutralize the supposedly acid soil that Karnak the Compost Bagger had decided this theoretical lawn was growing in. Nice; I had provided alkalinity to plants that require the most acidic soil of anything we grow. I left the dead bushes in the ground as a reminder of my extreme cleverness.
But despite their seemingly complete demise, they put out a couple of pitiful new leaves this Spring. So I began a coffee ground bucket brigade. Coffee grounds add up fast when you typically grind up four ounces of beans for a three-cup pot (I like it strong, OK?) and I was soon able to mulch each of the plants with a quart of grounds. They responded by turning a much more reassuring shade of green.
Each poor beleaguered plant has now received about a half-gallon of straight grounds, and each is now bright green and lush and growing rapidly. Not a single flower, but that was to be expected—and I'm not complaining. This is, in baseball terms, 'a rebuilding year', and I'm just happy that the fans are no longer coming to the park in mourning shrouds.
So if you have acid-loving plants that could use a boost, straight coffee grounds appear to do the trick. For plants like azaleas and rhododendrons that only flower once a Spring, feed after flowering and stop feeding by the 4th of July. If, like me, you're simply apologizing to plants you've killed, add up to a half-gallon of grounds slowly and evenly over the course of a season.
Oh, and take a lesson from my sad tale and never, ever use lawn fertilizer on blueberries. Unless you want to have your garden occupied by a beret-wearing peacekeeping force.