Coffee grounds could potentially hold the key to vibrant blue hydrangeas, as experts unveil the impact of coffee on flowers. A shot of java might just be what hydrangea blooms need.
In the world of gardening, coffee grounds have long been touted as a natural soil acidifier that could help change the colour of hydrangea blooms. However, a closer look at the facts reveals a more nuanced relationship between these two.
Firstly, it's essential to understand that coffee grounds, before being used in a coffee maker, are much more acidic than their post-brewing counterparts. This is due to the high concentration of acidic compounds found in coffee beans [1]. However, after brewing, coffee grounds become close to pH neutral, with a range of 6.5 to 6.8 [3]. This means that, contrary to popular belief, used coffee grounds do not acidify the soil enough to significantly alter the colour of hydrangeas.
The colour of hydrangea flowers is indeed linked to the pH level of the soil. Blue hydrangeas thrive in acidic soil (pH less than 7), while pink hydrangeas prefer neutral or basic soil (pH above 7), and purple flowers are produced in more neutral soil. However, relying on spent coffee grounds alone to achieve this acidity is ineffective [2].
Instead, coffee grounds are best utilised as part of a balanced compost mix rather than a direct soil acidifier. They provide valuable nutrients like nitrogen, potassium, and phosphorus, and improve soil structure and moisture retention [5].
So, what can gardeners do to change the colour of their hydrangeas? More dependable soil acidifiers such as aluminum sulfate or sulfur amendments are recommended for this purpose [4].
Amy Draiss, a hydrangea expert, advises using spent coffee grounds in a compost pile or as a soil amendment. She also notes that soil treated with spent coffee grounds can become more basic over the course of 2 to 3 weeks and then gradually decrease in pH after that [2].
Laura Walters, a Content Editor who joined the platform in 2021, provides gardeners with information in an easy and entertaining format. She never thought she would get paid to read and write about her favourite hobby, gardening. Interestingly, spent coffee grounds can help improve soil texture and prevent certain fungal diseases and bacteria [6].
It's worth mentioning that not all hydrangea varieties respond to soil pH changes in the same way. Certain varieties, such as mophead, lacecap, and mountain hydrangeas, can change colour depending on the pH level of the soil [7].
In conclusion, while coffee grounds offer numerous benefits to soil health and nutrient content, they do not acidify soil sufficiently to affect hydrangea flower colour noticeably. For altering hydrangea colour, more dependable soil acidifiers such as aluminum sulfate or sulfur amendments are recommended.
[1] https://www.sciencedirect.com/science/article/abs/pii/S0308527319316943 [2] https://www.gardeningknowhow.com/garden-how/soil-fertilizers/coffee-grounds-in-the-garden.htm [3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3739967/ [4] https://www.bhg.com/gardening/flowers/hydrangeas/how-to-change-hydrangea-color/ [5] https://www.thespruce.com/composting-coffee-grounds-1399367 [6] https://www.gardeningknowhow.com/garden-how/soil-fertilizers/coffee-grounds-in-the-garden.htm [7] https://www.gardeningknowhow.com/garden-how/flowers/hydrangeas/hydrangea-colour-change.htm
The benefits of coffee grounds extend beyond soil acidification, as they contribute to a compost mix with valuable nutrients like nitrogen, potassium, and phosphorus, improving soil structure and moisture retention [5]. Moreover, gardeners should consider using more dependable soil acidifiers like aluminum sulfate or sulfur amendments to alter the color of hydrangeas, as coffee grounds do not acidify soil sufficiently to affect hydrangea flower color noticeably [2].
