How to Reuse Coffee Grounds in Your Garden for Plant Growth (2024)

If you typically throw away your used coffee grounds, you may want to reconsider. Coffee grounds are a source of organic matter and can be added to compost or used as a fertilizer.

Organic matter from coffee grounds contains about 2 percent nitrogen and trace amounts of phosphorus, potassium, and micronutrients, such as calcium, magnesium, copper, iron, and zinc, which encourage healthy growth. Read on to learn how to use these nutrients from coffee grounds for plants in the garden.

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 (6.0 to 7.0) but others prefer acidic or alkaline soil. Therefore, scattering coffee grounds indiscriminately around all your plants is not a good idea.

Also, there is a difference between used coffee grounds, which are only slightly acidic, and fresh (unbrewed) coffee grounds, which have more acid and most of the caffeine content. In addition to not adding coffee grounds to plants for alkaline soil, 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, like roses, shrubs, and ground covers to trees. Acid-loving plants include azaleas, hydrangeas, magnolia trees, hollies, and beloved edibles such as blueberries and tomatoes.
• Plants for neutral soil are the happiest when the pH is around 7.0 In soil requirements for plants, you rarely see only “neutral” listed under pH requirements, almost every plant also has a tolerance for either acidic or alkaline soil, that’s why the pH is often listed as 6.5 to 7.5. Most garden plants fall into this category, including ferns and asparagus.
• Plants for alkaline soil prefer sweeter rather than acidic soil. These plants typically don’t benefit from coffee grounds unless you rinse them first to remove extra acid. Many perennials, including sedum, daylilies, hostas, geraniums, and aloe prefer alkaline soil.

Coffee Grounds in Compost

Adding coffee grounds and used paper coffee filters to your compost increases nitrogen, a composting material that aids growth. Coffee grounds also contain nutrients 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, but for compost, 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. When you don't have enough green material, the compost pile will not heat up. It's recommended that coffee grounds comprise no more than 20 percent by volume in compost to ensure various ingredients promote healthy and diverse microorganisms. Only add cool coffee grounds to compost, as heat can kill beneficial microbes.

Coffee Grounds as Fertilizer

Add composted coffee grounds directly to your garden soil by raking them into the top couple of inches of soil or simply sprinkling the grounds on top. However, make sure the layer is no thicker than 1/2 inch, and do not use them in areas where growing plants from seed, as coffee grounds can reduce germination rates and growth. Small amounts of coffee grounds mixed with dry materials will give up their nitrogen. Used coffee grounds are nearly neutral in pH, so they shouldn't cause acidity concerns.

However, be careful not to use too many coffee grounds at once. Coffee grounds can benefit soil drainage and aeration, but add grounds gradually to enhance garden soil. Too many coffee grounds pile up and lock together to create a water-resistant barrier in the soil. When mulching with coffee grounds, add a 4-inch layer of coarse organic mulch, like wood chips, to help protect the coffee grounds from becoming compacted.

Make a coffee ground "tea." Add 2cups of used coffee grounds to a 5-gallon bucket of water. Let the "tea" steep for a few hours or overnight. Use this concoction as a liquid fertilizer for garden and container plants. It also makes a great foliar feed sprayed directly on the leaves and stems of your plants.

Tips for Using Coffee Grounds

Using coffee grounds for your compost or as a soil amendment is not the only way you can repurpose them:

• Prevent pathogenic fungi: Bacterial and fungal species normally found on decomposing coffee grounds—such as non-pathogenic Pseudomonas, Fusarium, Trichoderma, and pin molds—prevent pathogenic fungi from establishing.
  
• Prevent bugs and pests: Coffee grounds can deter 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.

Possible Disadvantages of Coffee Grounds for Plants

One 2016 research study found that using spent coffee grounds in growing broccoli, leeks, radishes, violas, and sunflowers 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 inherent in the coffee grounds. If you aren't getting satisfactory results with coffee grounds, you may want to experiment with and without them in your garden.