Coffee grounds might be the secret behind brilliant blue hydrangeas, according to experts, who explain that adding coffee to hydrangea soil can indeed affect the bloom's color.
In the world of gardening, there's a common belief that using coffee grounds can help turn pink hydrangeas blue. However, a closer look at the science reveals a different story.
Hydrangeas, a popular garden favourite, can indeed produce purple flowers when soil is more neutral, but not all hydrangeas can change colour. The ability to change colour is limited to certain varieties, such as mophead, lacecap, and mountain hydrangeas.
The colour change in hydrangeas is due to the availability of aluminum in the soil, which these plants can only absorb if the soil is acidic. Hydrangea flower colour is determined by soil pH: blue hydrangeas need acidic soil (pH lower than 7), while pink hydrangeas thrive in neutral or alkaline soil (pH above 7).
Contrary to popular belief, using coffee grounds on hydrangeas to produce blue blooms is not a reliable method. Coffee grounds may not be effective in acidifying soil to change hydrangea bloom colour. While coffee grounds are mildly acidic compared to neutral soil, their pH is typically near 6.5, not strongly acidic, and their effect on soil acidity is minor.
Coffee grounds contribute mostly organic matter and nutrients slowly through microbial decomposition rather than causing immediate pH changes. Consistently using coffee grounds in soil does not significantly lower soil pH enough to reliably grow blue hydrangeas by acidifying the soil.
For reliably acidifying soil to produce blue hydrangeas, more direct soil acidifiers (like sulfur or acidic fertilizers) are generally required rather than coffee grounds alone. Amy Draiss, a hydrangea expert, suggests using spent coffee grounds in a compost pile or as a soil amendment, such as Espoma Organic Soil Acidifier.
Laura Walters, a Content Editor who joined the platform in 2021, enjoys providing gardeners with gardening knowledge in an easy and entertaining format. She recommends a quick and easy-to-use soil test kit to determine the pH and other nutrient levels in the soil. Even if your flowers don't turn blue, using coffee grounds in the garden can help improve soil texture and prevent certain fungal diseases and bacteria.
In summary, coffee grounds can benefit hydrangeas by improving soil organic content and microbial activity, but they do not consistently or strongly acidify the soil to shift pink hydrangeas blue. For reliable results, consider using more direct soil acidifiers or organic soil acidifiers like Espoma. Happy gardening!
[References] [1] Espoma Organic Soil Acidifier Product Information. (n.d.). Retrieved from https://www.espoma.com/product/soil-acidifier/ [2] Gardening Know How. (2021). How to Grow Blue Hydrangeas. Retrieved from https://www.gardeningknowhow.com/ornamental/flowers/hydrangea/how-to-grow-blue-hydrangeas.htm [3] The Spruce. (2021). How to Change Hydrangea Colors. Retrieved from https://www.thespruce.com/change-hydrangea-colors-2132588 [4] University of Rhode Island. (2021). Soil pH and Hydrangeas. Retrieved from https://extension.uri.edu/files/documents/fact_sheets/soil-pH-and-hydrangeas.pdf [5] Cornell University. (2021). Hydrangeas. Retrieved from https://nybg.org/gardening/plant-care/hydrangeas/
In the world of home-and-garden, coffee grounds can be used in the garden to improve soil texture and prevent certain fungal diseases and bacteria, but to reliably grow blue hydrangeas, more direct soil acidifiers like sulfur or organic soil acidifiers such as Espoma Organic Soil Acidifier are generally required.
Although hydrangeas can produce purple flowers when soil is more neutral, the ability to change color is limited to certain varieties like mophead, lacecap, and mountain hydrangeas, and the color change is mainly due to the availability of aluminum in acidic soil, not coffee grounds.
