Coffee grounds amend rose bush soil, helping to make it looser and promoting worm activity, since they enjoy coffee. Coffee grounds can deter garden pests like slugs, though they're not necessarily the best slug prevention. Coffee can also give slow-growing rose plants a perk.
Pet owners should stay away from coffee in the garden to prevent pet poisoning. While rose plants benefit from coffee, too much of a good thing is bad. Add 1 inch of grounds at a time and wait until they compose to add new material.
Coffee grounds can be spread on the soil directly or mixed into your compost pile, then applied as part of a compost. Coffee shouldn't take the place of fertilizer. Check with local cafes for coffee grounds or save your own grounds.