Peonies, with their shrub-like height and heavy-petaled flowers, can make wonderful backdrops to the flower garden. The sudden appearance of ants covering these plants distresses many new gardeners. The ants, however, are simply enjoying an easy meal and do not hurt the peony.
Peonies produce nectar along the edge of the bud scale.
Tiny nectaries, or specialized cells along the edge of the protective bud covering, produce a sugary sap. This sap draws ants, which soon cover the buds. Not every peony will attract ants, due to differences in the flavor or scent of the nectar. Not having ants on a bud is just as harmless as having a bud with constant ant traffic.
Ants leave when the peony opens.
Many gardeners still believe that ants are absolutely necessary for proper opening of peony buds. Iowa State University Extension, among other extension services, states unequivocally that the presence of ants has no bearing on the blooming of peony flowers.
Ants protect their food sources, whether when they shield honeydew-producing aphids or defend a particularly delectable fallen fruit. This is also true of peony buds; the ants often drive off insects that would otherwise damage the bud.