By: Adin Burwell, Elena Chatrchyan, and Zoe Loomis
Uses for Mulches
The United States is home to avid coffee drinkers. We consume 146 billion cups of coffee a year, which leaves behind a lot of spent/used coffee grounds. This waste can be repurposed outside your home as mulch! As a simple layer of material on the soil surface, mulches can help with weed suppression, erosion control, climate control and preventing compaction. Mulch prevents direct sunlight from striking the soil. This reduces weed growth and prevents soil overheating during the growing season. When used for climate control, mulches reduce water losses from evaporation and reduce your irrigation – saving time and resources. Organic mulches like spent coffee grounds will also serve as a slow-release fertilizer as they decompose.
How Much Mulch Do I Need?
While coffee grounds make great mulch, they work best when combined with other materials. When used alone, the small particles of coffee grounds can easily compact and restrict airflow and decrease water infiltration into the soil. Generally, an effective mulch layer is around 3 inches thick. However, with coffee grounds, it is best to combine a thin layer of coffee grounds (half an inch or less) with a thicker layer (up to 4 inches) of a more coarse organic material. Acceptable organic mulch options to include with the coffee grounds are tree needles, wood chips, and lawn clippings.
What Kind of Coffee Grounds?
Grounds from any type or brand of coffee are suitable as a mulch. What is important is that you are using spent, not fresh, coffee grounds. Using spent coffee grounds offers a cost-effective mulch option that helps to keep organic material out of landfills. Applying fresh coffee grounds (unused and right out of the packaging) to the soil can alter pH levels and damage your plants. There is no need to first compost the spent coffee grounds when using them as a mulch.
Where Can I Use My Coffee Grounds As Mulch?
Spent coffee grounds are effective as a mulch in home gardens, community gardens, and on lawns as well as on small urban farms that have access to this material. While coffee grounds could be used on a larger scale, the amount of material available is often limited, and there are other more widely available mulches.
Coffee Grounds and pH
While often said to be useful in acidifying soils, the effects of spent coffee grounds on soil pH are minimal. Using fresh coffee grounds can lower soil pH but also harm your plants. If you need to acidify your soil, a sulfur amendment from your local garden or hardware store is less expensive, simpler and more effective to use.
How to Apply Coffee Grounds for Weed Suppression
YEAR 1
Break the plot or cultivation area into 4 sections. Choose any section, and use coffee grounds as a mulch in one. Grow crops normally on the other 3 sections.
YEAR 2
Add coffee grounds as mulch to the next section over. Begin planting and cultivating the section that had coffee grounds the year prior.
YEAR 3
Repeat with new section.
YEAR 4
Repeat with final section.
Additional Resources:
Check out Washington State University’s bulletin on Coffee Grounds for more information.
For further information or if you have any questions, contact your local Cornell Cooperative Extension office or contact us at soil3@cornell.edu.