Coffee gives many a drinker that morning jolt that they’ve come to rely upon. Coffee detritus also can serve a similar purpose in the garden. Coffee grounds help fast-maturing vegetables and other acid-loving plants grow because they provide extra nitrogen, Master Gardener Dianna Morris reported in the "Utica Dispatch" in 2008. So instead of tossing those used grounds into the trash, consider using them as a garden mulch around certain plants and incorporating them into composts.
Tomatoes are heavy feeders that benefit from soil with a higher nitrogen content. A thin layer of grounds should be sprinkled around plants before it rains for a slow-release fertilizer, master gardener Diana Morris wrote in 2008 for the "Observer-Dispatch" in Utica, New York. Tomato plants feed more heavily as they are flowering and bearing fruit, so add grounds during that period.
Apply coffee grounds around the base of big leaf hydrangeas to change the bloom color from pink to blue. The bloom color depends on the soil pH. Alkaline soil will result in pink blooms, even on plants that originally had blue flowers. Blue hues are caused by a soil that is acidic. Sprinkle coffee grounds around the base of hydrangeas, not in the middle, to naturally amend the soil.
Conservatively apply coffee grounds around roses for a nitrogen boost unless the soil is already adequately acidic; too much nitrogen can damage plants. Otherwise, the grounds can act like fallen leaves decomposing. Add coffee grounds to a compost pile and apply that to gardens.
Form a coffee ground ring around lettuce to provide plants with more nitrogen and to deter pests, such as slugs, deer and rabbits. Mix the grounds into a new garden to promote growth of other fast-growing vegetables.
Add no more than a 1-inch layer of coffee grounds around acid-loving azalea bushes to promote blooms and vibrant color. When in doubt about the original soil acidity level, also add dried grass clippings or leaves on top of the grounds to create a more balanced nitrogen application.
Blueberry bushes, like azaleas, also grow best in soil that is more acidic than alkaline. Apply coffee grounds thinly around bushes to boost fruit production and deter pests. Avoid applying a thicker layer because the grounds have been shown to attract fruit flies in smaller spaces.