Controversy brewing
Like all young gardeners, I learned to appreciate the difference between clayey or sandy/porous soil versus friable soil you’d be glad to take home to mama. As I recall, I began gardening and drinking coffee at about the same time, a youthful idealistic time in which I intended everything I did would produce a positive butterfly effect to make the whole wide world a better place.
I saw coffee grounds as a valuable contributor to soil friability. There was no internet then, but there were articles and I was a reader. One article claimed the acidity of coffee grounds would benefit acid-loving plants such as strawberries, blueberries and rhododendrons. I didn’t know what a rhododendron was, but I liked strawberries, so – like a thurifer carrying a thurible to the altar – I daily bestowed the blessing of fresh coffee grounds (just dumped the grounds on the soil filter and all) around the strawberry patch and beyond.
There are articles online right this minute willing to name two dozen plants which “love” coffee grounds: roses, radishes, azaleas, hibiscuses, peppers, eggplants, hydrangeas and on and on. We are told the grounds are rich in nitrogen and offer acidity to plants that like it. These articles validated my nascent gardening instincts, and, obviously, I was not the only one.
Then, a couple weeks ago, along comes the article “Hold the Coffee” by respected, educated, field-tested botanist James Wong. He spent part of his career at the Royal Botanical Garden, Kew, an impressive place to work. His BBC television series Grow your Own Drugs became the highest-rated gardening show in England.
His article recounted how, for years, coffee grounds has been touted for lowering soil pH and adding nitrogen. He said, “It all sounds like such a brilliant idea: upcycling industrial waste into free, organic fertilizer. It is just a shame that in reality it is probably doing the exact opposite.”
He points out the fresh grounds are still packed with caffeine. Coffee bushes apparently use caffeine effectively to repel other plants – a natural herbicide. It’s called allelopathy. Caffeine in grounds leach into soil which negatively affects nearby roots. In fact, researchers have tested coffee grounds on farms in Brazil and Vietnam as an herbicide. Yikes! Plus, Wong said, grounds don’t necessarily add much acidity.
If I had had pants on, they would have been scared off. Can it be that years of focused diligence has been partially undermining my best intentions? Pshaw! My symmetry was being cusfloozled! Was I supposed to learn something new?
Oh my my… long-held convictions cleft asunder… what malevolence had I committed… who to believe?
It came to mind that some of the articles I had read through the years could have been cursory studies of other cursory studies. I decided to read further with Wong’s article in mind, and I found that Mother Earth News plowed the middle ground. It recommended letting coffee grounds cool down before simply adding them to compost. Mix with leaves, grass clippings, kitchen waste and turn occasionally for two or three months. Once composted, apply in thin layers to beds. No need to shovel it in.
The University of California Department of Agriculture conducted a study in which they added coffee grounds directly to a test plot but not another identical plot, planted identical plants in both, and monitored the results. Their report stated, “The study concluded that all of the plants grew poorly in response to the spent coffee grounds.” Nevertheless, the report recommends adding coffee grounds to compost.
If dried coffee filters blown all around the garden are any indication, I did several things (actually, everything) wrong with fresh coffee grounds, but I meant well. There’s a lesson far beyond coffee grounds in here somewhere.