Save Old Coffee Grounds To Fertilize These 7 Vegetables For A Thriving Garden

If you're the sort of person who needs to start the day with at least one cup of coffee in order to function, you probably throw out a lot of coffee grounds. But before you tip that filter basket into the trash can, did you know that vegetable plants — including corn, broccoli, and tomatoes — might benefit from the byproducts of your morning joe? With a bit of preparation and thoughtful application, your vegetable garden can reap several nutritional benefits from composted coffee as plant food. (And that bit of advice your well-meaning friend gave you about coffee grounds being acidic and lowering the soil's pH? A myth. The acid in coffee is water soluble and mostly ends up in the part you drink!)

Don't just dump hot grounds straight from the pot onto your plants. You'll need to age them for a few months in an outdoor compost pile — and make sure they're cool before you add them, or the heat could kill beneficial microorganisms. Once they've aged, apply a thin layer to the top of the soil, no more than ½ inch deep. Coffee grounds may improve the tilth, or structure, of soil. They may contribute small amounts of nitrogen, phosphorus, and potassium, as well as traces of other beneficial nutrients — but these nutrients won't be available for uptake by plants' roots until they've been properly composted. Make sure you're only adding grounds to mature, actively growing plants, as they can inhibit seed germination or even inflict nitrogen burns on young roots.

Cabbage (Brassica oleracea, Capitata group) might see improved growth and yields when you add composted coffee grounds. A cool-weather crop, cabbage is best grown in USDA Zones 2 through 11 in spring or fall. If you find yourself struggling to keep slugs away from your cabbages — they do seem to be a favored treat for the slimy invaders — you can use coffee as an all-natural bug repellent for vegetable plants. Drench the soil with a mixture of one part brewed coffee to two parts water, or spray the leaves with one part coffee to nine parts water.

Yes, tomato is botanically a fruit, but most people would culinarily consider it a vegetable. As heavy feeders that are especially hungry for nitrogen, tomatoes (Solanum lycopersicum) might particularly appreciate nitrogen-rich coffee ground compost. As an added bonus, coffee grounds can suppress certain fungal rots that can plague tomatoes, such as Fusarium. Just make sure to avoid using coffee grounds on delicate young plants. Tomatoes are grown as annuals in cooler climates, but in warmer areas such as zones 10 and 11 they might function as perennials. Plant them in an area with full sun and well-draining soil.

Another nitrogen-greedy crop, corn (Zea mays) benefits from an application of composted coffee grounds. The Fusarium-suppressing properties of coffee grounds — which are due to competition from the fungal species that work to decompose the grounds — might also help to combat root and stalk rot in corn. A full sun crop that favors warm weather, corn is hardy in zones 2 through 11. Keep in mind that in order to ensure adequate pollination, you'll typically need 12 or more corn plants together (maybe a good fit for someone who drinks a lot of coffee and produces a lot of grounds!).

If you've tried to grow broccoli (Brassica oleracea, Italica group) before and found that it had pale or discolored foliage and just didn't seem to be thriving, it's possible a nitrogen deficiency was to blame. Giving these heavy feeders a light blanket of composted coffee grounds might help them get a jump on forming that luscious crown. Broccoli tends to like well-composted, rich soil and, like many brassicas, cooler temperatures. Best grown in zones 2 through 11, you can start broccoli seeds indoors for planting in spring or fall. Keep it well watered or risk bitter-tasting heads.

In the case of lettuce (Lactuca sativa), using coffee grounds in compost might benefit you as much as the nutrient-hungry leafy greens — a study published in the Food Chemistry academic journal in 2019 found that lettuce grown in soil amended with composted coffee grounds increased its nutritional value of lettuce. Elements such as manganese, iron, and zinc appeared in greater concentrations in coffee-composted lettuce. Suited to zones 2 through 11, lettuce prefers full sun unless grown during summer heat ... in which case, it'll appreciate some afternoon shade, as high temperatures and dry soil can make for bitter leaves.

Hungry for both nitrogen and consistent moisture, cucumbers (Cucumis sativus) may benefit from the nutrients deposited by composted grounds, as well as the improvements to the soil's water retention and drainage. Hardy in zones 2 through 11, cucumbers favor slightly acidic soil in a site with full sun. Cucumbers love warm soil and thrive when the days are hot and the nights are warm. Wait until all threat of frost has passed before you plant your cucumber seeds. Make sure to harvest your cucumbers while they're still young, as they'll get tougher and grow larger seeds as they age.

A highly nutritious leafy green, kale (Brassica oleracea var. acephala) needs moist, well-draining soil rich in nutrients (especially nitrogen) — an ideal candidate for composted coffee grounds. Like its relative, cabbage, kale is also often at the mercy of slugs. You might consider creating a barrier of coffee grounds around your kale, which they may not be able to crawl over. Grow kale in zones 2 through 11 in full sun, preferably in the cooler weather of fall. In fact, hardy, cold-loving kale's flavor is improved by frost, and you may even be able to harvest it in the snow.