In small doses, coffee can help your plants thrive. 

By Tim Nelson
July 16, 2019

Sometimes you make a cup of coffee that you just can’t finish and feel guilty about it. Sometimes you empty spent coffee grounds into the trash and feel like there has to be a better way. 

Well, here’s some good news: on a micro level, if done properly, your leftover coffee can actually be good for your plants. Turns out, the nitrogen that’s found in coffee grounds can help blooming plants, especially those that thrive in relatively acidic soil. 

For example, coffee grounds can play a vital role when added to compost, especially if you’re worried about an overcrowded garden. Their caffeine content, while potentially harmful to a plant itself, can help to suppress the growth of other plants in a given area of the garden that would be competing with your chosen crop for resources like water, sunlight, space, and soil nutrients. 

Though we might find spent coffee grounds pretty unappetizing, that’s not the case for worms. Research both conducted and quoted by Washington State University suggests that earthworms “use coffee grounds as a food source,” and “pull coffee grounds deeper into the soil, [which] may account for noted improvements in soil structure.” The research also adds that fresh or composted coffee grounds “can be used in a mulch layer” and shouldn’t be used “in areas where you are growing plants from seed.” 

It’s not just the grounds that can be great, either. That cooled-down coffee you couldn’t finish could come in handy as well. The Spruce suggests that plants who love lower pH levels of soil (like African violets, rhododendrons, pines, etc) can occasionally be watered with cold coffee. Doing so about once a week (at most) seems to be the appropriate amount, and it won’t hurt to dilute that unfinished cup with some more water before you do. In fact, filling up a mostly empty coffee pot for use as an impromptu watering can might be your best bet. 

There are a lot of caveats to giving your plants a pour-over with coffee, however. Be vigilant when it comes to monitoring your houseplants: if their leaves start turning yellow, it’s a sign that they’re not a fan of the acidity. And ONLY pour diluted black coffee into that pot or your garden plot. Any extra flavors or add-ins like dairy or sugar are definitely going to do more harm than good. 

Is coffee some sort of miracle substance that will help you have the best garden around? Not necessarily. But if you take care not to just dump coffee grounds on a plant and take the time to understand how your crops will react to slightly acidic soil, it can help your plants (and, by proxy, you) blossom and reach their full potential. 

 

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