Q. Can coffee grounds be used as a fertilizer for houseplants?
Coffee grounds are a low-level source of nitrogen and a minor source of calcium and magnesium, so the grounds, especially when composted, can be an effective fertilizer for acidic outdoor plants.
For indoor plants, however, direct application of the grounds is not recommended. The fine grind typically used for brewing causes the grounds to pack down tightly, decreasing aeration, and providing a medium for fungal growth and a buildup of soluble salts.
You can, however, make coffee ground "tea." Add two cups of used coffee grounds to a five-gallon bucket of water. Let the "tea" steep for a few hours or overnight. You can then use this concoction as a liquid fertilizer.
A word of caution: fruit flies are attracted to coffee grounds, especially in enclosed compost heaps, where moisture is high--yet another reason to avoid using coffee grounds directly on indoor plants or composting with them indoors.
For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service