If you are both a coffee lover and a plant parent, you may be eager to recycle your coffee grounds while also potentially helping your garden or houseplants grow. While coffee grounds can benefit your plants, it’s not always as simple as dumping fresh grounds on top.
While brewed coffee is quite acidic, used grounds are pretty neutral, meaning that they likely won’t do much harm or good in terms of pH. However, the remaining caffeine in your coffee grounds could inhibit seed germination and growth. Plus, piling grounds on top of your plants may prevent air and water from properly circulating and soaking into the soil.
If used properly, though, coffee grounds can improve soil structure and may deter pests (and plant-loving cats). So what to do instead?
Add grounds to your compost or mulch
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An indirect approach will allow your plants to reap the benefits of your used coffee grounds without risking stunted growth. Mix grounds into your mulch or compost pile, which you can then use to boost your soil. However, make sure your entire compost bin isn’t made of coffee grounds—Treehugger recommends one part coffee to four parts other organic matter.
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Use directly in small amounts
If you don’t have homemade compost, you can sprinkle a small handful of grounds onto the soil and gently mix them into the first inch or two. Or you can make a “tea” for indoor and container plants using 2 cups of grounds to 5 gallons of water steeped overnight.
Add to your worm bin
If you have an earthworm compost setup, coffee grounds make great food.
The bottom line with coffee grounds in gardening: less is more, and indirect before direct. Don’t simply dump each morning’s grounds on your plants.