There are a few common reasons your hydrangea may not be producing blooms this year. These reasons include incorrect pruning, weather damage, improper fertilization and sun exposure.
Pruning:
Pruning hydrangeas can be a tricky thing; it requires knowing the exact variety of hydrangea you have. There are 2 types of hydrangeas when it comes to flower bud growth and development; those that produce buds on old wood and those that set buds on new growth. Old wood hydrangeas (Big Leaf, Climbing and Oakleaf varieties), set their flower buds in late summer for the following season. If you’ve pruned an old wood hydrangea anytime after the buds have set, you will have effectively removed all of your flowers for this year. Although you’ll be flowerless this season, if you allow your hydrangea to set buds this season you should have blooms again next year. However, if you removed a lot of branches from your shrub, it may take a couple seasons to see a full canopy of blooms again.
New wood hydrangeas set their buds on new growth so these shrubs should only be pruned in late winter or early spring to encourage vigorous new growth through the summer. If you prune a new wood hydrangea during the active growing season your shrub may set new buds but will most likely not have long enough to mature these buds before cold weather returns.
Weather Damage:
There are very few old wood hydrangeas that are tolerant to our cold Iowa winters. Because old wood hydrangeas set their blooms in late summer, those buds are exposed to the winter temps and risk freezing. If you suspect your hydrangea has succumbed to some frost damage, wait until all threat of frost has past, then cut back all damaged branches to maintain a tidy appearance. Though old wood growers run a higher risk of suffering winter damage, new wood hydrangeas can also be affected by cold weather if we receive an abnormal frost during the growing season.
Improper fertilization:
Fertilizer should only be applied to hydrangeas once in early spring and once again in mid-summer. Avoid using a fertilizer with a high ratio of nitrogen as this can encourage vegetative growth and suspend the development of flower buds. The easiest way to ensure you use the correct fertilizer is to look for one specifically formulated for hydrangeas. It is also important to note that hydrangeas may need a higher phosphorus ratio to encourage flower bud development.
Planting location:
Hydrangeas require around 4 hours of direct sunlight to bloom but Big Leaf, Mountain, Smooth and Oakleaf varieties will suffer if exposed to full sun. The best location for these hydrangeas is an area with well-drained soil that is exposed to several hours of morning sunlight with dappled shade from the harsh afternoon light. In contrast, panicle hydrangeas prefer a brighter sun exposure and require full sun to bloom well.