Research confirms what many gardeners already know: coffee grounds can be a useful addition to gardens and landscapes, primarily as a soil amendment, mulch, and composting ingredient.1
Believe it or not, coffee grounds are also great at boosting hydrangea blooms.
The acidity of coffee grounds influences not only the size but also the color of your hydrangea flowers, especially if you’re aiming for vibrant blue hues.
How it Works
Hydrangeas are unique in that their flower color can be influenced by the soil’s pH level. Acidic soil (pH below 7) promotes the absorption of aluminum, which turns hydrangea blooms blue.
Coffee grounds are naturally acidic and, when added to the soil, they gradually lower the pH, making it easier for the plant to absorb aluminum.
Benefits of Using Coffee Grounds
Coffee grounds offer a multitude of benefits for your hydrangeas that extend beyond their ability to influence flower color.
- Larger, More Vibrant Blooms: In addition to influencing color, the acidity in coffee grounds also contributes to overall plant health. Healthier plants produce larger, more robust flowers.
- Slow-Release Fertilizer: Coffee grounds are rich in nitrogen, an essential nutrient for plant growth. As they decompose, they release this nitrogen gradually, providing a sustained source of nourishment for your hydrangeas.
- Improved Soil Structure: Coffee grounds also improve soil aeration and water retention, creating a more hospitable environment for root development.
- Environmentally Friendly: Using coffee grounds is a sustainable gardening practice, as it repurposes a common household waste product.
Applying Coffee Grounds to Your Hydrangeas
Transform your coffee waste into beautiful blue blooms by incorporating coffee grounds into your hydrangea care routine.
- Collect Used Coffee Grounds: Save your used coffee grounds from your daily brews. You can also ask your local coffee shop for their used grounds, as they often have an abundance of them.
- Apply to the Soil: Spread a layer of coffee grounds around the base of your hydrangeas, working them into the top few inches of soil. Avoid piling them up directly against the stems.
- Repeat Regularly: For best results, apply coffee grounds several times throughout the year, particularly in the fall and spring. You can also add them to your compost pile.
- Monitor Soil pH: While coffee grounds are beneficial, it’s important to monitor your soil’s pH to ensure it doesn’t become too acidic. You can purchase a soil pH testing kit at most garden centers.
What to Remember When Using Coffee Grounds
While coffee grounds can be a fantastic addition to your hydrangea care routine, there are a few essential factors to keep in mind to maximize their benefits and avoid potential issues.
- Not All Hydrangeas Are Blue-Blooming: Some hydrangea varieties, like ‘Annabelle’ or ‘Limelight,’ are not affected by soil pH and will always produce white or lime-green flowers, respectively. Focus your coffee ground efforts on bigleaf hydrangeas (Hydrangea macrophylla) if you’re hoping to achieve blue hues.
- Patience Is Key: Changing the soil pH and seeing a noticeable change in your hydrangea blooms takes time. Don’t be discouraged if you don’t see immediate results. Be consistent with your coffee ground application and monitor your soil pH over time.
- Maintain a Balanced pH: While acidity is crucial for blue hydrangeas, excessive acidity can harm your plants. If your soil is already naturally acidic, or if you use other acidic amendments, consider incorporating lime to maintain a balanced pH level. Regularly test your soil’s pH to ensure it stays within the ideal range for your specific hydrangea varieties.
With patience and consistent application, using coffee grounds can be a simple and effective way to enhance the beauty and vibrancy of your hydrangea flowers.
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Nancy has been a plant person from an early age. That interest blossomed into a bachelor’s in biology from Elmira College and a master’s degree in horticulture and communications from the University of Kentucky. Nancy worked in plant taxonomy at the University of Florida and the L. H. Bailey Hortorium at Cornell University, and wrote and edited gardening books at Rodale Press in Emmaus, PA. Her interests are plant identification, gardening, hiking, and reading.