Gardeners often observe that peony buds are visited by large numbers of ants shortly before they bloom. Witnessing this, some have speculated that their presence is somehow necessary for the buds to flower. In fact, this is not the case; however, the ants’ presence may still be of benefit to the plants.
Ants are drawn to peony buds by a rich nectar secreted there by extrafloral nectaries at the base of the leaf stems. The belief emerged that the ants’ nibbling "tickles" or "unseals" the buds, allowing them to bloom. However, this is not the case: They can bloom whether or not ants are present.
As the ants’ presence is not essential to successful blooming, it may be tempting to kill them using insecticide spray on the basis that they are harmful or merely unsightly. However, this is unwise. The same spray will also harm vital pollinating insects, and with their numbers already dropping in many places, this is the last thing any gardener wants. Furthermore, insecticide buildup in soil and groundwater is a serious environmental problem.
Another reason to leave the ants be is that, even if it’s not essential, their presence does the buds no harm: They will eat the nectar in preference to the plants themselves. In addition, while there they may also eat other insects that would nibble at the plants. They are your allies, standing guard over your precious blooms-to-be!
Ants may be beneficial to the growing plants, but they hardly add charm once the flowers are cut and in a vase. There are a number of ways of removing ants from picked flowers without damaging the blooms. In some cases, a firm shake (outside!) will do the trick; otherwise, try carefully rinsing the blooms or using a soft brush.
There are a number of reasons why peonies may fail to bloom, ranging from frost and pests to soil quality and depth of planting. Peonies do not react well to transplanting, and this may interrupt their flowering. When ants do fail to appear it is likely to be a result of the problem, not a cause: If the buds’ proper growth is disrupted, they will not produce the nectar that attracts the ants in the first place.