Using coffee grounds in the garden seems like a no-brainer. After all, coffee grounds have the color and texture of loamy garden soil, and the grounds are make of plant material. In fact, coffee grounds are a free and nutrient dense source of soil enrichment in the flower garden. Use them as a compost amendment, add them directly to the garden as a soil enhancer, or even try your luck at repelling pests naturally.
Sources of Coffee Grounds
If you’re a coffee drinker, you may already be putting your coffee grounds to good use in the flower garden. However, if you’re the only coffee drinker in the house, or if you brew your coffee using a single brew machine, you won’t get much of a yield from this free source of organic riches. If you treat yourself to the occasional coffee shop treat, bring a large zip lock bag along and ask for the grounds on hand. If you have a close relationship with your local coffee purveyor, ask the manager to save the grounds for you to pick up a few times a week. If you don’t drink much coffee, gather the grounds from your office break room, grocery store deli, or restaurant.
What about coffee pods? The explosion of single cup coffee makers creates a barrier for collecting coffee grounds; after all, who wants to scrape grounds from tiny pods one tablespoon at a time? One solution is to consider purchasing fully compostable pods, which are growing in popularity as consumers demand an end to the plastic waste of single serve pods. Cameron's, Hill Bros., Juan Valdez, and San Francisco Bay OneCup are a few of the companies that produce compostable coffee pods. These pods will break down most efficiently in an active, hot compost pile with a temperature of at least 120 degrees F.
Types of Coffee Grounds
With respect to available garden nutrients, you can use regular or decaffeinated coffee. If you use decaffeinated coffee, consider the method used to remove the caffeine. For the organic purist, the Swiss water method is preferred. This method uses carbon or charcoal filters to remove the caffeine. The commonly used direct method uses chemical solvents to remove the caffeine, but the roasting process causes nearly all of the solvent to evaporate.
To support the efforts of organic gardeners in coffee growing nations, you may prefer to use organically grown coffee in your garden. Shade grown coffee further supports the ecosystem by maintaining the habitat of jungle birds.
Coffee Grounds in Compost
Although coffee resembles the carbon-rich brown leaves in your compost bin, coffee grounds count as green matter in compost making. You can add the filter to the compost bin along with the grounds; it breaks down quickly. Choose unbleached coffee filters for your drip coffee maker to minimize chemicals in the garden.
Worms also love coffee grounds, so use them freely in your vermicompost bin. Add the grounds, filters and all, directly to your bin. The moisture level should be that of a wrung out sponge to provide the optimal environment for your red wigglers. Because the grounds so closely resemble the worm castings, you should add other kitchen produce scraps (apple cores, salad trimmings) to serve as a barometer of the decomposition process. When the other scraps disappear, it's time to add more coffee grounds and veggie scraps.
Coffee Grounds as Mulch and Fertilizer
Combine coffee grounds with chopped leaves for a fluffy mulch you can use around your acid-loving plants. Avoid using coffee grounds as stand-alone mulch, as the grounds can form as water-repelling crust as they dry in the sun. Rhododendrons, heaths and heathers, azaleas, roses, and evergreen shrubs appreciate the acid content in coffee grounds, so you can also add the grounds directly to the planting hole for these specimens as a growth stimulant. If you’ve composted the grounds, you can use them anywhere in the garden, as the composting process neutralizes the acidic component of the coffee.
Coffee Grounds as a Pest Repellant
As much as we love the taste and smell of coffee, it has the opposite effect on most insects and animals. Some researchers speculate the caffeine has a toxic effect on sensitive animals; others say that the smell and/or texture deters the pests.
Coffee grounds work best against pests that crawl or come into contact with the ground. Aphids and beetles aren't bothered by coffee grounds, and caterpillars usually aren't either since they hatch from eggs laid on plants. However, snails and slugs will make a detour around grounds. Rabbits will also bypass flowers that use coffee grounds as a mulch. Refresh the grounds often, once or twice a week, to keep up the efficacy of the repellent, as coffee grounds break down into the soil quickly.