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Coffee Grounds in the Garden: Do They Actually Help Your Plants?
Eggshells, Calcium, and Blossom End Rot
My sister texted yesterday asking for my thoughts on planting eggshells with her tomatoes. I've read that advice before and feel that something has gotten lost in translation. Yes, tomatoes suffer without calcium, but when blossom end rot rears its ugly head, it's usually about absorption, not availability. Calcium is an immobile nutrient; it travels through the plant only with water, so consistent watering is critical. Without steady moisture, calcium can't reach the developing fruit.
But also, as a rule of thumb, I only add fully composted materials into the garden beds. I want the nutrients to be immediately available to the plants.
Should You Put Coffee Grounds Directly on Garden Beds?
So that got me thinking about brunch and another garden tip that I’d like to challenge. Coffee in the garden is lovely. Coffee on the garden isn't as wise. While it's often praised as a sustainable and budget-friendly soil improver, it's not as simple as dumping your morning brew, or its spent grounds, straight onto your beds.
I recommend skipping direct application. Used alone, coffee grounds can compact, forming a crust that blocks air and water. And as they break down, they temporarily tie up nitrogen in the soil, leaving plants stressed instead of nourished. One more small point: the caffeine can inhibit seed germination and seedling growth, particularly at concentrations of 0.1% or higher.
The Best Way to Use Coffee Grounds: Add Them to Compost
Despite their color, used grounds are high in nitrogen and count as a (fantastic!) GREEN in your compost pile. In order for that nitrogen to be available to our plants, the grounds must first decompose.
Add grounds to compost with a healthy mix of brown, carbon-rich materials like dry leaves and paper.
If You Still Want to Apply Coffee Grounds Directly
If you do prefer to apply directly, mix well into soil and balance with other organic material, and best to do in more mature, established landscape beds.
Last summer, I spoke with Homes & Gardens about this very topic. Read the article HERE.
