The powdery mildew problem is about the only drawback to peonies. Usually it doesn't happen until after they bloom and nearer to the end of the season when the sun angle starts to shift. A location in good sun that is not too crowded with other plants to allow for air flow to dry them faster after a rain or high humidity is helpful. I've found that if the mildew is caught very early and the peonies are sprayed with neem oil (and water solution - read the directions), it can reduce the amount of mildew and help the appearance of the plants. Severely mildewed leaves can be removed to slow the spread.
The powdery mildew problem is about the only drawback to peonies. Usually it doesn't happen until after they bloom and nearer to the end of the season when the sun angle starts to shift. A location in good sun that is not too crowded with other plants to allow for air flow to dry them faster after a rain or high humidity is helpful. I've found that if the mildew is caught very early and the peonies are sprayed with neem oil (and water solution - read the directions), it can reduce the amount of mildew and help the appearance of the plants. Severely mildewed leaves can be removed to slow the spread.