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Reconsider Using Coffee As Fertilizer For These Plants
By LIBBY THOMPSON
Coffee grounds make a great slow-release fertilizer for some garden staples, but plants sensitive to caffeine or preferring a more alkaline soil could react negatively to them.
In the vegetable garden, asparagus is sensitive to acidic soil and prefers a neutral pH of 6.5 to 7.0. Various herbs like lavender and thyme also prefer alkaline or neutral soil.
Fresh coffee grounds can also have a negative effect on flowers and trees. For example, lilacs and roses like pH between 6 and 7, and linden trees prefer pH between 7 and 7.5.
Similarly, arborvitae trees prefer pH between 6 and 8. Meanwhile, roses, lilies, and hydrangeas won't appreciate coffee grounds simply because they're sensitive to caffeine.