Use a knife to remove a small ring of outer bark about an inch wide all the way around the limb. Then, cover the limb with soil, leaving 6 to 12 inches of the tip growth uncovered. Old established hydrangeas may also be divided in the early spring by using a shovel to divide the clump. The most common reason for hydrangeas failing to bloom is winter injury. Other reasons may be too much shade, poor fertility and too much nitrogen fertilizer.
Hydrangeas are susceptible leaf spots and powdery mildew.
Insect pests on hydrangea include aphids, leaf tiers, rose chafers and red spiders. Blue Prince' 'Compacta,' supposedly more compact than 'Nikko Blue' with darker green leaves. Coerulea,' perfect flowers a deep blue and ray flowers blue or white. 8-inch leaves, which turn bronze in fall. The white flower clusters are 6 to 10 inches wide in lacecap effect.