If coffee is a staple in your daily routine, you’ve probably discarded plenty of coffee grounds. Surprisingly, these grounds are rich in organic matter and can be a fantastic addition to your compost pile, creating a nutrient-rich amendment. However, there are some misconceptions about using coffee grounds directly in your garden soil or with houseplants.
We consulted gardening and soil experts to clarify the best ways to utilize coffee grounds in your garden and why they shouldn’t be added to your houseplants. Coffee grounds are nutrient-dense and full of organic material but are often mistakenly labeled as a fertilizer. “Coffee grounds are indeed beneficial as a soil amendment, meaning they enhance the soil’s properties,” says Elizabeth Murphy, author of Building Soil: A Down-To-Earth Approach: Natural Solutions for Better Gardens & Yards. “Although they contain nitrogen and small amounts of other nutrients, their nutrient content varies, and they can’t be used in large enough quantities to meet all of a plant’s fertility needs. They aren’t a reliable fertilizer.”
Matthew Evans, author of SOIL: The Incredible Story of What Keeps the Earth, and Us, Healthy, explains, “Coffee grounds are composed of organic materials like cellulose and lignin, which decompose at different rates, making them a slow-release soil amendment.” He adds that coffee grounds need to be broken down by microbes first to release their nutrients. When preparing soil for planting, it’s common to add amendments like compost, humus, or manure to boost soil nutrients. A small amount of coffee grounds can also be incorporated directly into the soil. “Coffee grounds can be used in moderate amounts around plants,” says Evans. He recommends not spreading them more than 1-2 cm thick and in a band about 3 cm wide.
It’s also important to avoid placing coffee grounds directly in contact with plant stems or foliage. Evans suggests leaving a small gap, about half an inch, between your plants and the coffee grounds to prevent mold growth. Contrary to popular belief, coffee grounds don’t increase soil acidity. “Once brewed, coffee grounds are nearly neutral in pH, around 6.5-6.8, so they won’t acidify your soil,” explains Leslie F. Halleck, author of Tiny Plants and a Certified Professional Horticulturist. “Soils that are high in pH and alkalinity are difficult to acidify, even with genuinely acidic products.” Knowing your soil’s pH is crucial since plants need different nutrients and soil types for optimal growth.
If your garden plants are established, you can apply coffee grounds sparingly. “With coffee grounds, moderation is key, and observing your plants’ response is wise,” says Murphy. “A small amount can provide a nitrogen boost during the season, but too much can harm soil and plant life.” Nitrogen is vital for plants, but undecomposed coffee grounds won’t contribute nitrogen and might even deplete it. “Nitrogen is consumed during the decomposition process,” explains Halleck. Adding large amounts of undecomposed organic matter, including coffee grounds, can cause nitrogen deficiencies in plants. “Too much undecomposed organic matter can actually deprive your plants of nutrients,” she says.
Avoid applying coffee grounds directly to seedlings or soil where you’re sowing seeds. “Be cautious with young plants and seedbeds, as grounds can inhibit germination and root growth,” advises Murphy. The best way to benefit from coffee grounds is to compost them first, allowing them to break down fully and release their nutrients.
