Do coffee grounds effectively acidify soil?
Written by
Benjamin Miller
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.Coffee grounds provide some mild advantages for acidifying soil in the landscape. Coffee grounds have a pH of approximately 6.2 when fresh and approach neutrality as they decompose. These acidic benefits will be very temporary and surface-level. They will improve soil pH when used in conjunction with other organic amendments, such as elemental sulfur. The combination of coffee and elemental sulfur will raise the soil's acidic pH for a longer period.
Effective Uses
- Mulch: Thin layers suppress weeds while slowly releasing acids
- Compost booster: Accelerates decomposition in acidic compost piles
- Container plants: Mix sparingly with potting soil for small pH drops
Limitations
- Temporary effect: pH reduction lasts 2-4 months maximum
- Surface action: Only impacts top 1-2 inches (2.5-5cm) of soil
- Nitrogen tie-up: Microbes consume nitrogen during decomposition
Safety Tips
- Avoid thick layers: Prevents mold formation and compaction
- Keep from pets: Caffeine harms dogs if ingested
- Balance nutrients: Supplement with nitrogen fertilizer if needed
Mix coffee grounds with amendments that complement them. Please put them in compost piles alongside oak leaves to get the benefits of the balanced acidity. You can layer it under a mulch of pine needles for added permanency of the pH effect. This method will lead to slow and steady acidification while improving the texture and nutrient content of the soil.
The response of different plants to coffee grounds varies. Blueberries and azaleas are the most beneficial and should receive regular applications of coffee grounds. Hydrangeas will also respond favorably and exhibit more blue flower color. Avoid using near alkaline-loving plants, such as lavender, that may suffer from acidic build-up around the root zone.
Ensure you collect the grounds appropriately for your gardening purposes. Fresh, moist grounds will work best, as opposed to dried grounds. Local cafes will typically discard large quantities of grounds daily; check with them. Store grounds in sealed containers to prevent mold from collecting before you can use them. Make sure you always rinse away salt residues before using grounds collected from espresso machines.
Make sure to monitor how the plants respond to the application of coffee grounds. Look for signs of nitrogen deficiency, such as leaf yellowing. If a deficiency does occur, you can counter it with organic sources of nitrogen. Check the soil pH in every season to see if it changes. Careful monitoring will help ensure the acidification strategy is applied on an ongoing basis with minimal unintended consequences.
Read the full article: 10 Acidic Soil Plants That Thrive
