Quoting article: Many people feel that coffee grounds lower the pH (or raise the acid level) of soil, which is good for acid loving plants. But this is only true for unwashed coffee grounds. “Fresh coffee grounds are acidic. Used coffee grounds are neutral.” If you rinse your used coffee grounds, they will have a near neutral pH of 6.5 and will not affect the acid levels of the soil. Qstn: terms confusing. When writer says "unwashed coffee grounds," does he mean dry grounds not yet used to make coffee? Does he mean what is left in the filter after making coffee is good only as organic material, not good for lowering pH?
Coffee Grounds to Lower pH
I guess Favof and I will agree to disagree on this one. Check out the GardenMyths website on this topic: http://www.gardenmyths.com/coffee-grounds-acidifies-soil/
I think the author means to rinse or not rinse the coffee grounds which have been brewed.
fresh used coffee grounds are around PH 5-5.5 , so they are truly lower than the natural level,
coffee grounds pH levels depending on the conditions in which they are left to decompose. The closer they are into soil, the quicker they move to pH neutral level,
so the earlier you add them to the soil, the quicker for them to decompose to be closer to neutral level.
but if you leave the used coffee grounds on its own for half a year under sunlight and rain, its PH level would be close to PH 6. then you can add to the soil, worms in the soil would help the PH level speeds up by creating vermicast from coffee grounds, these casts are at pH levels around 8.5 to 9.
all in all, most plants can benefit from the adding of organic matters and that includes coffee grounds despite its varied PH levels.
I had a friend who poured leftover coffee on her plants. This slowly acidifies the soil. Coffee grounds already used to make coffee should be added to the compost pile. I hope this answers your question. Like you, I find "unwashed coffee grounds" to be a confusing term.