Coffee grounds good for plants are a rich source of nitrogen, a nutrient necessary for plant growth. They can be added to soil or compost for an extra boost of this essential nutrient.
However, Rosser warns that a layer of used grounds can prevent water penetration and air circulation. She recommends a balanced approach to houseplant care, including appropriate watering and a well-rounded fertilizer regimen.
Nutrient-Rich Soil Amendment
Using coffee grounds as an organic soil amendment provides a good source of nitrogen for plants, which is an essential nutrient needed for growth and to make chlorophyll, the green pigment that gives flowers their color. This nutrient is also important for healthy leaves and stems. Coffee grounds can be tilled directly into the soil, added to compost or used to create a coffee-based fertilizer that can be applied to plants as a spray to give them a boost of nitrogen for a period of time.
Other nutrient rich soil amendments include manure from cows or horses, chicken/rabbit droppings, mushroom compost and vermiculite. Organic matter is beneficial for enhancing soil texture, improving water retention and creating a healthier environment for microorganisms to thrive in. Organics are not readily available to plant roots as they are a slow release natural fertilizer and require microorganisms in the soil to change them into soluble nutrients for the plants to absorb.
Another popular soil amendment is coir from coconuts, which is a renewable alternative to peat moss and sphagnum moss that holds water well in the ground and improves soil aeration. It is also a source of nitrogen and other nutrients and contains natural nematicide and fungicide properties.
Natural Pest Repellent Properties
Natural pest repellents are a good alternative to toxic chemical sprays that can contaminate the environment. They are biodegradable and nontoxic to pets, children, and wildlife, and they don’t leave harmful residues on plants or soil. Natural products also help prevent the development of resistant pests that are commonly targeted by commercial pesticides.
Lavender is a natural insect repellent that can be used to deter a variety of pests, including moths, flies, mosquitoes, and rodents. It is also an effective antifungal and can be used to fight fungal diseases such as powder mildew.
Basil is another aromatic herb that is effective at repelling a number of pests, including flies and mosquitoes. It is also a useful culinary herb and can be grown in the garden to add fresh flavor to recipes.
Garlic is also a useful natural pest control method. Its strong odor deters a wide range of insects and can be placed around entrance doors and windows to keep pests from entering the home.
Catnip can be planted as a companion plant to tomatoes, beans, and cucumbers to repel aphids. It contains nepetalactone, which is known to have insecticidal properties and can be used as an alternative to synthetic pyrethroids.
Soil Structure Improvement
While many recommendations for using coffee grounds to fertilize plants are anecdotal, research suggests that they provide some benefits. First of all, they can lower soil pH. Adding composted coffee grounds to your garden improves soil structure by loosening it, allowing better movement of water and air.
This is particularly important in poor soils that are heavy and compacted, as they are in most urban gardens. They can also help prevent plant diseases. Experiments have shown that a layer of decomposed coffee grounds suppresses some disease organisms in vegetable crops.1
Coffee grounds contain nitrogen-rich “green” materials essential for plant growth, as well as a variety of other compounds, including indigestible sugars and cellulose, which add structural support to the soil. They can be mixed with other organic materials, such as fruit scraps and vegetable peels, to create a rich compost that will help enrich your garden.
Adding used coffee grounds to your garden is safe, especially once they have been fully composted. If you are going to use them as a fertilizer, however, it is best to sprinkle them on the soil surface sparingly and avoid making a thick layer that may block water penetration and inhibit root growth.
Enhanced Microbial Activity
Coffee grounds are a great addition to compost, and they also make an excellent fertilizer. They’re high in nitrogen and other micronutrients, including potassium, magnesium, calcium and copper. They can be added directly to soil or used to create a liquid fertilizer.
The key is to apply the spent coffee grounds sparingly. Too much can prevent the water and nutrients from penetrating the soil. Also, it can be too acidic for plants that need alkaline soil.
As a general rule, avoid adding fresh or uncomposted coffee grounds to the garden. Even though they’re considered organic matter, fresh and uncomposted coffee grounds are extremely acidic. If added directly to the garden, it can kill off beneficial bacteria in the soil and reduce the microbial activity that’s so necessary for healthy, productive plants.
However, if you have a compost pile, coffee grounds are an excellent source of organic matter and can be added to the compost heap at any time. They also help to loosen soils and minimize compaction, improve drainage and aeration, increase nutrient-holding capacity and stimulate root growth. Composted coffee grounds are a good choice for potting mixes as well. In fact, many potting mixes contain up to 30 percent finished compost.
Acidification of Soil pH
Coffee grounds are a natural source of nitrogen, but as they decompose, their nutrient content falls off. Therefore, they should be added to soil as a fertilizer only in small quantities, and only after thoroughly composting.
They also slightly acidify the soil, which is good for flowers such as roses, hibiscuses, begonias and peonies, which prefer to grow in slightly acidic conditions. They can be used on shrubs, perennials and vegetables as well, but if growing carrots or tomatoes, be sure to get a soil test first because adding a lot of organic matter can actually decrease the pH.
Composting the coffee grounds is the best way to use them, but they can be added directly to the garden in small quantities as well. Just be careful not to add too much, because the coffee can prevent water from reaching the roots of plants.
Some gardeners have reported that the scent of the grounds repels slugs, snails and other pests. Other gardeners have had no luck with this, and the effectiveness of the spray can vary with weather conditions and seasons. Coffee can also be mixed with soil in containers and pots to help increase water retention. Just avoid using it on succulents or other plants that prefer to be dry.
Sustainable and Eco-Friendly Gardening Practice
Using coffee grounds as fertilizers is a great way to recycle this widespread byproduct of caffeine consumption while helping the environment. They contain organic material that improves soil and act as a nitrogen source for plants, as well as other nutrients like potassium, phosphorous, and micronutrients.
In the garden, it’s a great way to increase nutrient availability for any plant that is in need. A general rule is to mix spent grounds with other compost ingredients like shredded leaves, straw and grass clippings for best results. This ensures a balanced blend of “wet” and dry materials to speed up the decomposition process.
The acidity of the grounds can alter the pH level in the soil, which can be beneficial for some types of plants, particularly hydrangeas. These plants are typically pink, blue, or white and will bloom a more vibrant color in a soil that is below a pH of 6.
Many gardeners make their own compost by piling green waste from the kitchen and yard with brown material, like dried leaves and twigs, to encourage microbial activity and break down the material into a rich soil amendment. Adding used coffee grounds to this compost increases the nitrogen content, which is why they work so well as a slow-release fertilizer.
Considerations for Proper Application and Dosage
Coffee grounds contain nitrogen and other micronutrients that are slow to release into the soil, making them a good fertilizer for plants. They also help lower soil pH, which makes them great for acid-loving plants like roses, azaleas and hollies.
But be careful when using grounds around other plants. Their low pH can affect them, especially if they’re applied in large quantities or for prolonged periods of time. Also, applying them in large quantities to soil can lead to a dense top layer that prevents water and air from reaching the roots.
If you want to use grounds as a fertilizer, mix them into compost or potting soil with other materials such as dried leaves, grass clippings or shredded newspaper. You can also apply them to the surface of the soil as a mulch. If you’re going to mulch with coffee grounds, however, make sure the soil underneath isn’t clay because the particles can clump together and form an impenetrable barrier that will keep nutrients from reaching the roots.
You should also avoid using ground coffee as a soil amendment for vegetables because it can cause the soil to become too acidic. Research your garden’s preferred pH level and consult a garden book or local Cooperative Extension Service before using it in the vegetable patch.