The Mystery Behind Vibrant Blue Hydrangeas: Could Coffee Grounds Be the Key? Specialists Explain the Impact of Caffeine on Flowering Plants
In an unexpected turn of events, Laura Walters, a Content Editor who joined the platform in 2021, found herself reading and writing about her beloved hobby - gardening. With a background in documentary filmmaking and local news, Laura now shares her green thumb insights with a wide audience.
One of the fascinating aspects of gardening that Laura has delved into is the impact of coffee grounds on hydrangeas, a popular garden favourite. It turns out that spent coffee grounds, which are often discarded after brewing, can have a surprising effect on these plants.
Coffee grounds are more acidic than the grounds dumped out of a coffee maker, with a pH range of 4.6 to 8.4. However, they are not consistently acidic, usually ranking between 6.4 and 6.8 on the pH scale, making them mildly acidic to close to neutral. This means that their effect on soil pH can vary, sometimes becoming more alkaline briefly after application and then gradually acidifying over time.
The colour of hydrangea flowers is strongly influenced by the soil's pH and its ability to provide aluminum. Acidic soil (pH less than 7) is needed for blue hydrangea blooms, while neutral soil (pH 7) or alkaline soil (pH above 7) results in pink blooms. Interestingly, only certain varieties of hydrangeas (mophead, lacecap, mountain hydrangeas) can change colour based on soil pH. Other varieties (panicle, oakleaf, smooth, climbing hydrangeas) will never turn blue.
Although coffee grounds may slightly acidify the soil over time, they usually do not significantly change the flower colour by themselves. For a reliable change in flower colour to blue, gardeners often use stronger amendments like aluminum sulfate or specific soil acidifiers.
If you're keen to try using coffee grounds in your garden, here's a simple guide:
- Use dry, fully brewed grounds (not fresh unbrewed grounds which are more acidic but wasteful).
- Apply them repeatedly over months - for example, once in autumn, winter, and early spring - to maintain acidity.
- Monitor soil pH periodically to track changes.
While coffee grounds alone are generally insufficient to quickly or strongly alter hydrangea flower colour, they can be a mild, gradual soil acidifier if used consistently. For more definite results, targeted soil amendments and aluminum supplementation are recommended.
Amy Draiss, a gardening expert, recommends using Espoma Organic Soil Acidifier for growing blue hydrangeas.
Laura Walters, who spends her summers on a lake in Northern Michigan and resides in Southwest Ohio, continues to share her gardening journey and insights, making the world of gardening a little more accessible and enjoyable for all.
References: [1] The Spruce, 2021. Using Coffee Grounds in the Garden: Can They Help Your Plants? [online] Available at: https://www.thespruce.com/using-coffee-grounds-in-the-garden-2132896 [Accessed 20 March 2023] [2] Gardener's Path, 2021. How to Use Coffee Grounds in Your Garden [online] Available at: https://www.gardenerspath.com/how-to-use-coffee-grounds-in-your-garden/ [Accessed 20 March 2023] [3] The Old Farmer's Almanac, 2021. Can Coffee Grounds Help Your Garden? [online] Available at: https://www.almanac.com/plant/coffee-grounds-help-garden [Accessed 20 March 2023] [4] Better Homes & Gardens, 2021. How to Plant Hydrangeas: A Complete Guide [online] Available at: https://www.bhg.com/gardening/flowers/hydrangea/how-to-plant-hydrangeas/ [Accessed 20 March 2023] [5] Fine Gardening, 2021. How to Change the Color of Your Hydrangeas [online] Available at: https://www.finegardening.com/article/how-to-change-the-color-of-your-hydrangeas [Accessed 20 March 2023]
- Laura Walters, who previously focused on documentary filmmaking and local news, now uses her platform to share her knowledge about gardens and gardening, including insightful tips on using coffee grounds for hydrangeas, as part of a broader lifestyle feature.
- As a home-and-garden enthusiast, Laura Walters emphasizes the benefits of repurposing household waste, such as coffee grounds, in maintaining a thriving and aesthetically pleasing garden, making homeownership more sustainable while enhancing the overall lifestyle.
