Coffee grounds as mulch? Don’t do it!

I get coffee grounds from my local coffee shop. Can I use them directly on the soil as mulch (without mixing anything into it except to rake it into the soil)? The grounds are wet when I get them from the coffee shop. Should I let them dry out a little before putting it on the soil?

In just about every listing of “ingredients” for a successful compost pile, you’ll find coffee grounds among the nitrogen-rich kitchen waste “green” ingredients that make up the mix. But it’s a mistake to use coffee grounds alone. They are very acidic, and over time will change the pH of the soil – the measure of its acidity or alkalinity – to the point that plants that prefer alkaline soil will suffer.