The benefit of using coffee grounds as a fertiliser is that it adds organic material to the soil, which improves drainage, water retention and aeration in the soil. The used coffee grounds will also help microorganisms beneficial to plant growth thrive as well as attract earthworms.
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.
Use of non-toxic substances and no depletion of natural resources
High-value reuse and recycling
Longer lifespan, longer use of product and recycling of previously useless waste