Oregonians love their coffee (and not exclusively, I know). We brew it at home or get it on the run. There are coffee “stands” everywhere, chains and local artisans. Standalone kiosk drive “thrus,” corners of the local grocery market, bookstores, craft stores, public library, gas stations, or even a knife store (totally serious). All kinds (latte, Americano, cappuccino, and the like), flavors, milk types (cow, soy, coconut), and organic or not. Caf or decaf. Single-, double-, or triple-shot. How did coffee get so complicated?
There is simplicity to be found in all this coffee hype and jargon – the lovely leftovers – coffee’s little sister – the wondrous grounds. My dear maternal grandmother saved her stove-top percolator’s grounds, dumping the pot’s basket into an old metal coffee can she kept in a kitchen cupboard. Once full, her garden inherited the dark brown stash. As a child I asked her why she saved what so many simply put in the trash. “For the worms in the garden.”
Worms are very fond of coffee grounds and wonderful for your soil!
Maybe she knew or maybe not, but worms are not the only reason to indulge your garden with coffee grounds. The worms do seem to love them, and attracting earthworms (aka nature’s plow) to your soil is great for improving soil structure by loosening the soil, which aids with aeration and water permeability. Never mind the benefits of their super nutrient-rich castings (fancy word for worm poop).
Coffee has a pH of 5 while the spent coffee grounds (SCG) are reported to have a pH of about 6.9 or 6.2. Or 5.2 … or even less. Make up your mind, you say? Not so simple. There are authors and labs sure of their numbers but obviously in conflict. So for now, moderation until I can get back to you with the real scoop. That is if I can find it. I do use grounds in my compost (not more than 10 to 20 percent of the volume), add some to my worm bin, and dig some into the ground around my acid loving plants. Coffee filters can be added into your compost too!
Spent coffee grounds have many uses in the garden.
Quick pH lesson for those inquiring minds: pH is short for potential Hydrogen. Pure water is neutral with a pH of 7. Less is acid, more is alkaline (basic). My dad used to talk about soil being either sweet (alkaline) or sour (acidic). He would add lime to his lawn every spring to “sweeten it up” and improve the growing conditions.
We have clay soil here and that, combined with our rainy weather, equates to lime being leached out and a more acidic soil. Now, some plants not only don’t mind that lower pH but thrive in it. Which explains why we have so many happy azaleas, rhododendrons, ferns, trilliums, dogwoods (Cornus), camellias, Pieris japonica, hydrangeas, and blueberries (Vaccinium). Foxglove (Digitalis purpurea), astilbe, bleeding heart (Dicentra), and heathers (Calluna vulgaris) also are among the many that thrive in acidic soils.
Other benefits of using SCG in your garden:
Coffee grounds have low amounts of nitrogen, phosphorus, potassium, calcium, sulfur, boron, copper, iron, manganese, sodium, chloride, zinc and magnesium. Not in any special order.
They also seem to suppress common fungal wilts and rots during decomposition.
Sprinkled around your plants – there are claims SCG will keep snails and slugs (gastropods) at bay. I think there has to be a decent swath for this to work. The slimy critters don’t care for crushed eggshells, either.
Some folks say grounds will repel cats and lessen the likelihood of your garden bed being used as a litter box.
Grounds are a great way of adding organic matter to improve soil structure.
According to some studies, composted grounds are better for your plants and shrubs and have less potential detrimental effects secondary to acidity.
Rhododendrons are one of the many plants that prefer an acidic soil.
Other plants that will grow in acidic soil:
Acid-loving herbs and vegetables include cilantro, endive, garden peas, garlic, parsley, peppers, potatoes, radishes, rhubarb, soybeans and sweet potatoes.
Those that prefer only a slightly acid growing environment are beans, broccoli, cabbage, carrots, celery, corn, cucumbers, onions, squash, tomatoes and turnips.
What experience have you had using coffee grounds in your compost and/or garden? Want to weigh in on the pH debate?
Until next time, keep diggin' it!