Do you feed your roses with coffee grounds, considering it an eco-friendly life hack?
It's time to sound the alarm: In 2023, the Journal of Soil Science published a study showing that caffeine in soil blocks iron absorption by roses.
Renowned gardener James Wong told The Modern Gardener podcast:
"Coffee grounds for roses are like alcohol for a child. Minimum benefit, maximum harm."
The story of Irina from Novosibirsk became a lesson for thousands of summer residents: her hybrid tea roses, which she “treated” with coffee for three years, became covered with yellow spots and stopped blooming.
Laboratory analysis showed that the soil pH had dropped to 4.3, making it toxic.
“Coffee acidifies the soil, and most roses need a neutral environment,” explained agronomist Alexey Volkov in the blog “Pink Paradise.”
Scientists from Purdue University have found that even 100 grams of coffee grounds per bush reduce the immunity of roses to powdery mildew. But there is a nuance. Varieties grafted onto rose hips are more resistant.
An experiment by the Garden Expert channel showed that roses planted in soil with coffee, but with the addition of dolomite flour, bloomed 20% more abundantly.
“You can neutralize the acid, but it’s better not to risk it at all,” the presenter concluded.
The alternative? Use used tea. A study by the Royal Horticultural Society confirmed that tannins in tea leaves inhibit fungal infections.
Japanese gardeners from the Kyoto Roses nursery have been burying tea bags under their bushes for decades - their roses are considered the healthiest in the world.
But the main secret came from France. Winegrower Pierre Dubois accidentally discovered that roses growing next to grapes tolerate coffee fertilizing much better.
"Grape roots secrete alkali, balancing the pH," he wrote in his memoirs. Feedback from the "Roses without Chemicals" chat: "I replaced coffee with tea - the bushes came back to life in a month!"
Author: Valeria Kisternaya
