If you are used to tossing the grounds from your morning coffee every day, you might want to reconsider. With coffee grounds, you have a fabulous source of organic matter right at your fingertips. The grounds can be added to the compost or used as a fertilizer. The organic matter in coffee grounds includes minerals like nitrogen and phosphorous that benefit plants by encouraging healthy growth.
Coffee doesn’t only give you the jolt of energy you need for weeding and pruning; the spent coffee grounds can also be put to use. Read all about using coffee grounds for plants, whether indoors or in your garden.
Coffee Grounds in Compost
Adding coffee grounds and used paper coffee filters to your compost increases nitrogen, a green composting material that aids growth. Coffee grounds also contain minerals like phosphorus, potassium, magnesium, and calcium.
There are two types of compost material: brown and green. Items that contain nitrogen are considered green. Other green compost materials include food scraps and grass clippings. Your coffee grounds may be brown in color, but in compost jargon they are green material,
In compost, coffee grounds must be balanced with brown compost material, which includes dry leaves and newspapers. Use a 4-to-1 ratio of brown compost material to green compost material. If you add too much green material, your compost bin will start to smell. If you don't have enough, the compost pile won't heat up.
Coffee Grounds as Fertilizer
Add coffee grounds directly to your garden soil in your garden by raking them into the top couple inches of soil or simply sprinkling the grounds on top. In smaller amounts, especially when mixed with dry materials, coffee grounds will give up their nitrogen. Used coffee grounds are actually nearly neutral in pH, so they shouldn't cause concerns about their acidity.
However, be careful not to use too many coffee grounds at once. Coffee grounds can benefit drainage and aeration but the best way to enhance garden soil is when it's done gradually. When coffee grounds pile up. the small particles can lock together, creating a water- resistant barrier in the soil.
You can also make coffee ground "tea." Add 2 cups of used coffee grounds to a 5-gallon bucket of water. Let the "tea" steep for a few hours or overnight. You can use this concoction as a liquid fertilizer for garden and container plants. It also makes a great foliar feed you can spray directly on the leaves and stems of your plants.
Tips to Use Coffee Grounds in Your Garden
Using coffee grounds for your compost or as a soil amendment is not the only way you can repurpose them:
- Feed your worms: Add coffee grounds to your worm bin every week or so, as worms love coffee grounds. Just don't add too many at once, because the acidity could bother your worms. A cup or so of grounds per week for a small worm bin is perfect. In addition to using coffee grounds in your worm bin, earthworms in your soil will also be more attracted to your garden when you use them mixed with the soil as fertilizer.
- Keep pests away: Create a slug and snail barrier. Coffee grounds are abrasive, so a barrier of grounds placed near slug-prone plants may just save them from these garden pests. However, be warned that some researchers quibble with this advice and don't think it is effective. You may want to have a backup plan in mind if it doesn't work. Many cats dislike the smell of coffee grounds and may avoid using your garden as a litter box if you mix coffee grounds into the soil.
Which Plants Are Coffee Grounds Good For?
Soil pH is crucial for plant health, but the pH requirements are not the same for all plants (and the only way to know your soil's pH is by conducting a soil test). Most plants will grow well in a slightly acidic to neutral pH (between 6.0 to 7.0) but others prefer acidic or alkaline soil. Therefore, scattering them indiscriminately round all your plants is not a good idea.
Also, there is a difference between used coffee grounds, which are only slightly acidic, whereas fresh (unbrewed) coffee grounds have more acid; they still have most of their caffeine content as well as the acid. In addition to not adding coffee grounds to plants for alkaline soil, there coffee grounds should never be used on seedlings or very young plants, as caffeine can stunt their growth.
The pH preference of a plant tells you whether it can benefit from coffee grounds:
- Plants for acidic soil need a pH below 7.0. You’ll find plants of all kinds on this list, from flowering perennials and shrubs to groundcovers and even trees. Acid-loving plants include azaleas, hydrangeas, magnolia trees, and hollies, as well as beloved edibles, first and foremost blueberries and tomatoes.
- Plants for neutral soil are the happiest when the pH is around 7.0 In soil requirements for plants, you rarely only “neutral” listed under pH requirements, almost every plant also has a tolerance for either acidic or alkaline soi, that’s why the pH is often listed as 6.5 to 7.5. The majority of garden plants fall into this category, including ferns and asparagus.
- Plants for alkaline soil are the sweet-tooth plants (alkaline soils, as opposed to acidic soil, is also referred to as sweet). These plants typically don’t benefit from coffee grounds unless you rinse them first to get rid of the extra acid. Many perennials, including sedum, daylilies, hostas, geraniums, and aloe prefer alkaline soil.
Possible Disadvantages of Coffee Grounds for Plants
One 2016 research study found that using spent coffee grounds in growing broccoli, leek, radish, viola, and sunflower resulted in poorer growth in all soil types, with or without additional fertilizer. The good news is that the coffee grounds improved the water holding capacity of the soil and decreased weed growth. The researchers think the poorer growth was due to the plant-toxic compounds naturally present in the coffee grounds. If you aren't getting the results you hoped for with coffee grounds, you may want to try your own experiments with and without them in your garden.
What bugs hate coffee grounds?
Coffee grounds have been reported to deter bees, wasps, fleas, and mosquitoes, as well as slugs and snails. The coffee grounds can be used as is; it is not required (and might even be hazardous) to burn them before scattering them around your garden.
Can you add coffee grounds to potted plants?
Yes, it's possible, but it should not be more than a thin sprinkling. If you add too much, the coffee grounds will form a dense layer on the surface of the potting soil that is impenetrable to water. On a regular basis, using leftover coffee to water your potted plants is a much better idea.
When should I put coffee grounds on plants?
There is no hard-and-fast rule how often you can put coffee grounds on plants. The amount, on the other hand, matters a great deal. Unless you thoroughly rake the coffee grounds into the soil each time, you should not sprinkle more than a thin layer around your plants, or else the coffee grounds will become impenetrable and water will just run off instead of reaching the roots. If you evenly sprinkle a week's worth of coffee grounds around the plants and beds in your yard at the end of the week, it will likely not add up being more then a dusting, and that's fine.
Coffee Grounds and Composting. Oregon State University Extension Service.
Muratova, Svetlana A. et al. The Effect Of Caffeine In A Nutrient Medium On Rhizogenesis Of The Rubus Genus Plants. BIO Web Of Conferences, vol 23, 2020, p. 03013. EDP Sciences, doi:10.1051/bioconf/20202303013.
Hardgrove, Sarah J., and Stephen J. Livesley. Applying Spent Coffee Grounds Directly to Urban Agriculture Soils Greatly Reduces Plant Growth. Urban Forestry & Urban Greening, vol 18, 2016, pp. 1-8. Elsevier BV. doi:10.1016/j.ufug.2016.02.015