Dividing & Transplanting needs: Hydrangeas that grow into bushes with multiple stems, such as the bigleaf and smooth hydrangea, are the best candidates for dividing. In the North, divide hydrangeas in spring while the shrub is still dormant. In the South, divide in spring or fall after all the leaves have dropped. Water the shrub well. With a sharp spade, dig around the root ball and eventually remove the shrub from the ground.
Using the spade or knife, cut the shrub into 2 to 4 sections depending on the size of the plant. Make sure you have a solid mass of roots with each division. Replant each division in a similar location and keep the new plants well watered all season.
Pests/ Disease: Hydrangeas are generally insect and disease free plants. However, they can occasionally be attacked by aphids, spider mites and Japanese beetles. Reduce nitrogen fertilizer to thwart aphids and knock them off the leaves with a strong spray of water from a hose. Keep plants well watered to avoid spider mites. Hand pick Japanese beetles or set up hormone traps placed 200 feet away from the hydrangeas to draw the beetles away.
While hydrangeas may get leaf spots caused by various diseases, powdery mildew is probably the most prevalent disease. Powdery mildew causes a whitish film to form on the leaves. It eventually causes the leaf to yellow and die. If occurring late in the season, don't worry about it. Simply clean up the dropped leaves well in fall. If it needs control, spray Neem oil earlier in the season. You can also use a home remedy of 1 tablespoon baking soda, 1 tablespoon horticultural oil, in 1 gallon of water. This is a preventive spray that stop powdery mildew from forming.