01/09/2014 using left over coffee grounds for roses and other plants that like a boost in nitrogen is a natural way to add fertilizer to your garden plants without the. Coffee grounds add extra acidity to the soil around hydrangeas. Do Hydrangeas Like Coffee Grounds On a chemical level, this increased acidity makes it easier for the plant to absorb naturally occurring aluminum in the dirt. Do coffee grounds help hydrangeas . Coffee grounds turn soil more acidic, helping hydrangea blossoms turn blue rather than the typical pink or white. Some gardeners report success in turning their hydrangeas blue by applying coffee grounds to the soil. Coffee grounds add extra acidity to the soil around hydrangeas. The acidity of the grounds provides the key element, though aluminum sulfate or eggshells also produce the same effect. Coffee doesn't have any affect on whether hydrangeas bloom or not. They also help to keep the soil moist, which hydrangeas particularly enjoy. H...