How to Use Coffee Grounds to Improve Your Garden
“I know that coffee grounds are beneficial to soil, but in some places I read that they should be used in compost formation only. Some other sources claim that coffee grounds should be simply mixed with regular soil, including in existing pots. Which is correct? In some places, I also read that coffee grounds will deter pests after being sprinkled around the perimeter of a raised bed. Is that true?” – Reuven Koter, Minneapolis, MN
If coffee grounds are useful for gardening then we are truly in luck. Not only could you recycle the aftermath of your coffee for utilitarian purposes, but you would have a virtually endless supply of this valuable substance on hand at your neighborhood coffee shop whether it’s in St. Paul, Duluth or Minneapolis Minnesota.
It turns out that not only are coffee grounds useful for horticulturists, but coffee shop baristas will often set them aside for you so that you can pick them up at no cost. Ask your local coffee spot about it: Bring a 5-gallon bucket in the morning, talk to the manager, and by evening you might have a full bucket to pick up and take home. In the event you grind your own whole bean coffee, save the excess grounds in keep them in the freezer for preservation until ready.
Cultivating & Harvesting Coffee Matters
Coffee grounds, properly utilized, can benefit both the composting process and the building of soil structure. The question becomes how much to mix or apply in each circumstance. With a “bottomless cup” supply of coffee grounds at your fingertips, the temptation is to use more than you should and then you might suffer for having indulged in too much of a good thing.
The benefits of coffee grounds derive from their texture and chemical composition. Their texture is attractive to soil-improving earthworms that crave gritty fare in their diet. Earthworms benefit soil by improving its porosity through their tunneling activity and they add fertility through their castings, a euphemism for worm poop. Worm castings contain 12 of the 16 mineral elements plants require. Castings are also rich in humus – the end product of plant or compost decomposition — that adds sponginess to soil structure and deters pathogenic soil microorganisms. Humus makes quick-draining soil more water retentive and opens up compacted soil so that water drains through.
Whole Bean Coffee Is Multi-purpose
If you are interested in using your leftover coffee grounds to enrich your soil, let them make up one-fourth to one-third of the soil volume. Dig your grounds into the soil at a depth of 6-10 inches with the help of a rototiller or a spade (flat-blade shovel). While the grounds contain 2.28% nitrogen, most of it is not in an immediately usable form.
It is rather made gradually available to plants over time in the manner of slow-release fertilizer. As for the presence of other elements in coffee grounds, Soil and Plant Laboratory in Bellevue, Washington, analyzed used Starbucks coffee grounds and reached the conclusion that their incorporation into the soil “will substantially improve availabilities of phosphorus, potassium, magnesium, and copper and will probably negate the need for chemical sources of these plant essential elements.”
Where composting is concerned, coffee grounds can make up as much as one-third of the volume of your compost pile. Recall that compost piles consist of greens, notable for their nitrogen content, and browns that are almost entirely carbon.
Browns – fallen leaves, straw, newspaper, shredded paper, coffee filters — are the primary energy source of the decomposing bacteria you wish to attract to the pile, while nitrogen-containing greens – vegetable and fruit peels, fresh grass or leaf clippings, and farm animal manures — are a source of nutrition for these same bacteria.
The color of the material does not necessarily classify it as green or brown since coffee grounds, cow manure, and alfalfa hay are not green but classified as green due to their nitrogen content.
Of course, you will want to thoroughly mix the coffee grounds into the pile since if they are clumped on the surface (of either compost pile or soil), they will just sit there and attract fungus molds. When properly mixed into the pile, coffee grounds will quickly raise the temperature to 135 degrees — heat is generated by proliferating bacteria populations in response to nitrogen in the grounds – a degree of heat that kills weed seeds, grubs, and pathogenic microorganisms present in the pile.
There are certain myths associated with coffee grounds.
One is that they acidify the soil. The acid in coffee grounds is water-soluble and that’s why the coffee we drink is acidic. However, the grounds themselves have a nearly neutral pH so they will not lower the pH of garden soil.
Another myth is that their grainy, abrasive texture will deter soft-bodied slugs but investigations into this matter have proven otherwise. And don’t spread them in a bed where you are sprouting seeds since they have been found to depress germination.
Finally, coffee grounds should never be used as mulch because they will just soak up a lot of water (imagine peat moss being used as mulch), get moldy, and defy decomposition. Of course, if coffee grounds are an ingredient in finished compost, there is no problem with including them in your mulch or, for that matter, your potting soil.
The vast majority of commercially grown coffee plants are continuously drenched in pesticides. Most health experts, however, do not consider this a concern since unlike heavily sprayed lettuce and apples, for example, that we eat raw and are therefore more of a health issue, coffee beans are seeds of a fruit, the pulp of which is discarded. Coffee beans are also fermented, dried, and roasted at 400 degrees, processes that remove pesticide residues.
Still, if you want to drink coffee from beans grown on unsprayed trees, select Ethiopian brands. They do not use synthetic fertilizers because of the expense involved and so, de facto, nearly all Ethiopian coffee could be classified as organic. It is also true that since the coffee plant (Coffea arabica) is endemic to Ethiopia – meaning that its habitat is restricted to that place and that it grows wild nowhere else on earth — it is almost certainly more resistant to diseases and pests in its native land than it would be in other parts of the world.