Coffee Grounds and Roses

One of the best kept secrets in rose gardening is coffee grounds.  Most people know they’re good compost, but have no idea of what they’ll do for the soil in your rose garden.

In the March/April 2011 issue of the American Rose there was an excellent article called “A Cuppa Joe”, by Paulette Mouchet of Acton, California, which was the best explanation of using grounds in the garden I've seen.  Here is an excerpt:

“What makes coffee grounds so wonderful in the garden anyway?  Earthworms love them.  They make a decent fertilizer.  You can use them as mulch or as a green ingredient in the compost pile….  Organic gardeners know that earthworms are essential to a healthy garden.  When it comes to improving soil structure and water-holding capacity, earthworms can’t be beat….  While earthworms will eat most any organic matter, coffee grounds are like earthworm candy.”

But here’s the best part for rosarians.  The article goes on to say that Sunset magazine sent a batch of Starbucks coffee grounds to a soil and plant laboratory in Washington State for analysis.  Turns out that the pH of Starbucks grounds is a slightly acidic 6.2, which is right in the middle of the pH range we’re shooting for in growing roses. And that’s not all: they’re also a slow-release fertilizer with 2.28% nitrogen, .06% phosphorus and .6% potassium.

The trick in using coffee grounds is getting hold of a lot of them.  Unless you only have one or two roses in your garden, the grounds from your home coffee maker just won’t cut it.  Fortunately, that’s not a problem.  Starbucks has a policy to recycle their coffee grounds, whenever they can.  So you can walk into any Starbucks, get a really good cup of Joe, ask whether they have any grounds available for your garden, and walk out with a 30-pound bag of fresh grounds.  I recommend going around mid-morning, because they’re just past their biggest rush of the day, have a lot of fresh grounds all bagged up, and aren’t too busy to pack them up for you.  Once the Starbucks folks know you want them, they’re happy to give them to you.  To put this in perspective, I have put several hundred pounds of grounds in my mulch pile over the winter.  That mulch will be going on my roses all summer and when I mound my roses for winter protection in the fall, a substantial proportion of the mulch I use will be composted coffee grounds.

I also use fresh grounds as part of my regular fertilizing regimen.  I mix the Twin Cities Rose Club's great organic “Bob’s Mix” fertilizer with wet, fresh grounds, right out of the bag, in a 50/50 ratio, putting about two or three big scoops of the fertilizer-grounds mixture on every plant.  One other benefit:  It makes “Bob’s Mix” smell better!  And the roses love it.

There’s more in the “American Rose” article, as well, such as how coffee grounds repel slugs.  I put them directly into my hosta bed last summer and didn't see any more slugs, so I think that works too.  In short, coffee grounds are an excellent all-around component in an organic gardening regimen and they are very available to all gardeners, so it’s a real shame to see them go into the trash.

Springtime is a great time to get started putting coffee grounds in your mulch pile and directly on your plants as they're getting started for the season.  So get on down to your local coffee shop, tell them you're a rose gardener and ask them for a big bag of grounds.  Your roses will act like they're highly caffeinated!

Jack Falker

March 17, 2013