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Hardiness Zone: 5a
Dawn from Elmira, NY
I'm glad you asked this question. Most gardeners assume that because it's slightly acidic, fresh coffee grounds or leftover brewed coffee can be sprinkled over the soil of any acid-loving plant. Not true. It's actually a bit more complicated than that.
First of all, not all acid-loving plants are created equal. Plants like Azaleas, Gardenias,Hydrangeas, Roses, Rhododendrons, and Blueberries all seem to respond well when grounds are mixed in with their soil.
Acid-loving African Violets, on the other hand, do not. Most edible garden crops also prefer slightly acidic soil, but adding coffee grounds also seems to affect them in different ways.
For example, lettuce seems to benefit greatly from the addition of coffee grounds, but tomatoes are actually affected somewhat negatively.
Plant scientists are not exactly sure why some acid-loving plants respond differently to fresh grounds than others, but it could be because coffee contains allelopathic chemicals that actually inhibit growth in some plants.
This might be helpful when you're trying to control weeds, but unfortunately, coffee grounds can't tell the difference between the plants you like and the plants you don't.
Secondly, mixing fresh grounds in with the soil has a tendency to tie up some of the nitrogen while the grounds decompose. Once the fresh grounds are fully broken down, however, a modest amount of nitrogen is released back into the soil. Mixing small amounts into the soil probably won't affect your plant's nitrogen uptake too much, but it's still better to add the grounds after they have fully decomposed or just sprinkle a small amount on top of the soil.
Finally, a word of caution on using coffee grounds for houseplants: Moist grounds encourage fungus growth that can be detrimental to your plants. If you use them on houseplants, do so sparingly and avoid watering your plants unless the soil is dry to the touch.
Unfortunately, there's no real recipe for how much is too much. Your safest best is to add leftover coffee and used grounds to the compost pile (it's unlikely you could add too much).
If you don't compost, you'll have to rely on trial and error. A cup or two around shrubs and a tablespoon or two around potted plants now and then should do no harm.
Because coffee is somewhat acidic, adding grass or leaves (browns) as mulch can help neutralize its acidic affects around plants that prefer more alkaline soil.
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Which plants like coffee grounds?
Hardiness Zone: 8b
By JM Skinner from Jax, FL
Just to let everyone know, I have 75 tomato plants in pots. They are doing great, 3 ft. tall and growing. I used coffee grounds and organic fish and bat guano. Everything in my garden is organic, including the dirt.
I water my plants every two days in the evening and always at the same time. This is very important if you want your crop to produce. Timing is everything
Tomatoes are one.
Anything that is acid loving. Most plants that bloom, if they are delicate, give them less. Fuchsia' would be one of those.
Ixora plants, wegilia, Azalez-all acid plants will benefit from Coffee grounds.
Garden mint. We got a French press coffee maker. All last winter I would scrape out and empty most of the grounds, then run water in it to rinse the dregs of grounds and pour them out of the kitchen window onto the mint below. I couldn't believe my eyes when the huge deep green lucious mint came up in the spring. It was half way through the summer, and we were drinking iced mint tea like crazy, and lovin' it, when it finally dawned on me that they loved the coffee grounds that were in the dregs each day. I guess I'l leave the screen off the window :)
Do hibiscus plants thrive with coffee grounds?
What about hibiscus ?