Can coffee grounds effectively improve soil quality?
Written by
Kiana Okafor
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.When properly managed, coffee grounds can provide valuable nitrogen benefits while also enhancing and improving soil quality. Their high nitrogen content will benefit plant growth, yet must be balanced with high-carbon materials. When fresh, they temporarily bind nitrogen while undergoing decomposition and then may starve the plants. Composting the grounds before use will address this issue, while also preserving their nutritional value.
The acidity of coffee grounds warrants some consideration. Freshly ground coffee typically has a pH range of 6.5 to 6.8, which is slightly acidic. This is why acid-loving plants, such as blueberries and azaleas, will benefit directly from using them. For neutral pH plants, however, the grounds should be used in combination with crushed eggshells or wood ashes to achieve a neutral pH level. I have found the best results by mixing equal parts of dried leaves with coffee grounds.
Preparation Methods
- Compost for 2-4 weeks before application
- Mix with brown materials at 1:1 ratio
- Dry grounds before storage to prevent molding
- Screen large chunks for uniform texture
Application Techniques
- Spread thin layers (¼ inch) around plants
- Incorporate into top 2 inches of soil
- Avoid direct contact with plant stems
- Combine with mulch for slow release
The nitrogen content makes the grounds valuable, but this requires a carbon balance to be maintained. The grounds have a carbon-to-nitrogen ratio of about 20 to 1 and will require the equal addition of brown materials. Use shredded paper or straw to prevent nitrogen from being blocked from the plants. Properly balanced in the compost pile, the grounds release nitrogen slowly over a period of 4-6 months.
Earthworm activity increases significantly with the addition of coffee grounds. The worms will devour coffee grounds, providing for better soil aeration. I observed 30% more worms in coffee-ground-amended beds compared to the controls. This change in worm activity may lead to natural tillage methods that improve soil structure without disrupting the soil with mechanical tools.
To prevent soil compaction and water repellency, apply the product sparingly. A maximum of 20% of total compost and/or composted material is optimal. Too much ground coffee will crust, limiting water infiltration. Allow for a 6-8 week interval between each application to facilitate full integration.
Read the full article: Soil Organic Matter: The Essential Guide
