posted 3 years ago
I've used spent coffee grounds extensively. Yes, wet used grounds will clog. If you spread it out on a tarp for a few hours in the sun it will evaporate off enough moisture to use in the method you present.
However, I have applied used coffee grounds as a surface mulch and quite frankly it sucks. Even a small covering will dry into a thin crust that then repels water. If you hit it with enough water over a long enough period it will eventually loosen up, but then it explodes with mold, dries back into a crust and you're at square one all over again.
You can avoid this pain by applying the grounds to the soil, and then incorporating it into the soil with a shuffle hoe or similar implement. Even a hard tine rake will do it. It's extra work but it will save you a gallon of tears later on.