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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 Janet 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
Can I use coffee grounds on my house plants? I have a Christmas catus and a climbing plant that I am not sure what it is, other than it has large waxy leaves. I hate to throw them out and I can't compost them because I live in a apartment.
You can put a sprinkling of the grounds around your plants.
There are different opinions about using coffee grounds on house plants but most agree that using them outside (not heavy quantity in one place) is a good thing. Since you live in an apartment I see no reason why coffee grounds would be okay to use but do as Judy says and just sprinkle them on top of soil and not on the plants or the stems. Be sure to "sprinkle" as too much may become moldy.
Also, very weak black coffee/tea can be added (small quantities) to many plants as this seems to benefit my house plants more than coffee grounds.
This question has been asked on ThriftyFun before so here is a link that you might like to check out.
My best advice is not to add too much to indoor plants because they will definitely get moldy. I found this out the hard way :) If you use it, dig it in deep. It will be great.
So many terrific answers and good advice! My two cents?
Coffee ground is coffee beans (seeds) that have been roasted, not roasted to the point of turning into coal but still roasted enough to resist decomposing just like wood coal doesn't decompose. It is better to leave it on the ground when used with plants. It does get molded but if you scratch the coffee ground to air it the mold goes and coffee ground is untouched, just like coal, it doesn't mold. And that is the big problem. I experienced putting a lot of coffee ground in the soil of an indoor plant. I saw the plant decline after a few months and decided to quickly changed the soil. The coffee ground was there, it had not mixed with soil and had not decomposed at all. So as the plant can only benefit of the azote, phosphore and potassium once coffee ground has decomposed and these elements have gone into water to be absorbed by the plant the benefit is not big but the risk to damage the plant roots by roting them is important. The coffee ground and the water around it really stank as sewer water. This is what I am doing since I had this bad experience : I put coffee ground around the foot of the plants in the garden to protect the plants from insects and snails. To use the azote, phosphore and potassium for my indoor plants I put the coffee ground in a bottle of water once it reaches the bottom of the bottle I water my plants with the water only and not with the coffee ground. When it doesn't colorate the water anymore I throw the coffee ground away and I put new one in. I only do it once a month and I only water the plant that are not cultivated for their flowers as main interest because is azote is the main element of coffee ground and azote is more useful to plants cultivated for the beauty of their leaves. You do not have this kind of problem with tea leaves because tea leaves have been dried only. They decompose quickly and give good results as well.