I’ve recently tried mixing the used coffee grounds in baking soda, and I’m seeing a very visible chemical reaction. I haven’t tried putting it in the ground yet though.
Coffee grounds aren’t very good fertilizer, they still need to decompose. Better to mix them in your compost pile and wait til the compost is finished to use it.
Regarding acidity, like the other guy said, used grounds aren’t very acidic. But ultimately, the pH question is going to depend on lots of factors, including the pH of your existing soil and the optimum pH of the plants you’re growing. Sometimes you want to add acidic amendments. Where I live, there’s so much calcium carbonate in the soil, no amount of acidic compost would even make a dent in the pH
Sounds like the acidity doesn’t need to be neutralized. It’s recommended here that you compost them or just mix them into the soil. When I worked in coffee shops we would compost them and then someone picked that up. Also says some plants react better to coffee grounds but you shouldn’t have to apply baking soda because “Fresh coffee grounds are acidic. Used coffee grounds are neutral.”
Just compost them. No need to add baking soda unless you want your soil to be light and fluffy like pancakes.
They’re high in nitrogen and when mixed with carbon based materials will make excellent compost/soil amendment in 6-12 months. Shorter if you hot compost or bokashi.
I’ve mixed hundreds of pounds of used, fermented grounds into my 1100 sq ft. of loamy clay soil over the last three years. Some plants love it, a few don’t. I had the soil tested at the beginning and end of the three years and it didn’t change the pH significantly. The grounds start to sour, ferment and grow fungi as soon as a day after being stored, so get it out in the garden as soon as possible.
Oh that’s interesting. I noticed the mold as well when I leave it out. Could I grow mushrooms on it?
I don’t know enough about myco propagation to answer. I know they need rich organic matter. I always mix my grounds with composted cattle manure, food scraps and straw.
Sorry I’ve been asleep at the wheel for this community.
Anyway, there is a lot of good info here in the advice you already got.
Coffee grounds aren’t acidic, and their pHs are typically 6-7 which is fine. pH usually doesn’t start becoming an issue until it approaches 5.
Further, grounds have a great C:N ratio, which means they will decompose relatively fast in the soil, and won’t tie up N like other amendments do.
