I received the following question from a correspondent who had recently attended one of my presentations on vegetable gardening:
I have a question about using coffee grinds around my roses, gardenias, etc. We talked about it, but I don't remember if you said how OFTEN we can put coffee grinds out there. Can you help me with that?
M., in Scottsdale, Arizona
For coffee grounds, I’d go ahead and put them out as often as you like; they won’t harm the plants in anything less than truly massive quantities. You might use a small garden cultivator to scratch them into the soil a bit to aid decomposition and to head off the formation of any water-resistant layer. Coffee grounds are somewhat hydrophobic and in larger quantities can form a barrier to water penetration.
If you produce more than about a cup of coffee grounds each day, you may want to a) seriously think about how much coffee you're drinking; and b) run them through the compost pile before putting them in the garden. Coffee grounds are relatively high in nitrogen (with a carbon to nitrogen ratio of about 20:1, the same as grass clippings), and in our desert conditions much of that nitrogen is lost when applied directly to the soil. Compost is a far more stable product and less likely to result in nitrogen loss. Plus, paper coffee filters can go straight into the compost pile along with the spent grounds, where they will tidily decompose. Littering your yard with undecomposed filters is likely to attract the opprobrium of neighbors.
I hope this helps,