Effect of Coffee Grounds on Soil

Used coffee grounds are an excellent natural fertilizer for your garden. You can add them to both new and existing plant beds. The grounds can also help in eliminating certain pests, such as slugs, snails, and ants. If you drink coffee at home, you can use the grounds from your own kitchen. If you don’t drink coffee or need a larger quantity, visit your local Starbucks. The company has a policy of giving away used coffee grounds to customers for use in home gardens.

Benefits of Coffee Grounds on Soil

Coffee grounds are rich in nitrogen, calcium, and magnesium—nutrients that are beneficial for your plants. Using coffee grounds is an environmentally friendly and cost-effective way to nourish your garden. By recycling this household waste, you’re also helping to reduce landfill waste. The grounds can also improve your compost pile by helping to maintain the nitrogen balance, which is crucial for the decomposition of organic materials.

In addition to providing nutrients, coffee grounds increase the acidity of the soil. This is especially beneficial for acid-loving plants, such as azaleas, blueberries, and rhododendrons. However, be cautious—coffee grounds can harm plants that do not thrive in acidic soil. It’s important to apply grounds only to plants that can benefit from the increased acidity and avoid using them on others.

Coffee grounds can also improve the texture of the soil. They make it easier to till, which is especially helpful for vegetable gardens. The grounds attract worms, which can help aerate the soil. As worms consume the grounds and move through the soil, they distribute the nutrients and improve oxygen flow to plant roots.

Some studies suggest that coffee grounds may repel pests like slugs, snails, and ants. One study by the USDA found that coffee grounds are effective against slugs, while other studies have shown no significant difference in pest control. The caffeine and acidity in the grounds are thought to be the key factors in repelling these pests. There is ongoing debate among gardeners about the effectiveness of this benefit, with some swearing by it and others seeing little to no difference.

How to Add Grounds to Soil

There are several ways to incorporate coffee grounds into your garden.

Sprinkle Around Plants: You can sprinkle the used grounds directly around the plants in your garden. Lightly cover the soil and then water it in. This method allows the nitrogen to be gradually released, enriching the soil over time. Be sure to spread the grounds evenly—don’t pile them up, as this can cause the grounds to cake, forming a crust that prevents moisture from reaching the roots.

Work into the Soil: For an alternative method, you can lightly mix the grounds into the soil around your plants. Use a small garden spade to work the grounds into the top inch of soil. This helps prevent the grounds from compacting, ensuring better absorption and improved soil nutrition.

Add to New Plant Beds: If you’re preparing a new plant bed, add coffee grounds before planting. Till the grounds into the top 6 to 8 inches of soil to ensure an even distribution of nutrients. After adding your plants, backfill with the soil and grounds mixture. Water the bed well to help release the nitrogen.

Make a Liquid Fertilizer: Coffee grounds can also be used to make a liquid fertilizer for your plants. Mix four parts water to one part coffee grounds in a bucket and let it sit in the sun to warm up. This step is important because water that is too hot or too cold can shock the plants. Once it’s at the right temperature, spray the mixture onto your plants.

If you’re using coffee grounds to deter pests, there are a few different methods depending on the type of pest you’re targeting.

Repelling Slugs: Create a ring of coffee grounds around your plant beds to deter slugs. Some gardeners add crushed eggshells to enhance this effect.

Repelling Ants: For ant hills, mix one pound of coffee grounds with one quart of warm water for each ant hill. Pour the mixture directly onto the hill. Repeat the process for each hill on your property.