One of my favorite summer flowers is the old-fashioned, pompom shaped Hydrangea macrophylla. I can remember as a child being drawn to the cool shaded area on the north side of the house where my mother had a bank of blue hydrangeas planted. The giant blooms were as big as my head and such a clear, deep blue they seemed to belong in a velvet lined jewel box rather than casually hanging about the garden.
Old-fashioned hydrangeas are easy to grow if you follow a few simple guidelines. Most varieties are cold hardy to zone 5, which means they will tolerate minimum winter temperatures between -10 and -20 degrees F.
Hydrangeas are traditionally known as shade garden plants, but too much shade can result in reduced bloom production. Ideally they should be situated in areas of light shade to partial sun. If you live in a cool climate you can even plant them in full sun.
Hydrangeas are woodland plants so they prefer to be in consistently moist, well-drained, humus rich soil. A generous application of mulch will help keep the roots cool and retain moisture. Little pruning is required with old-fashioned hydrangeas. In fact, improperly pruned bushes can result in bushes not producing any blooms. Old-fashioned hydrangeas set their flowers on previous year's growth, or what is referred to as old wood. So, in late summer and early fall, your shrub is preparing blooms for next year.
In early spring you can tidy up the plant by removing any dead wood and old flower heads.
Any severe cutting back should be done immediately after the flowers fade in the summer.
Other causes for lack of bloom include harsh winter temperatures, warm spells followed by cold weather, and late freezes. All can damage or kill tender flower buds. If you site your plants in a north or east facing area of your garden, you can reduce the chances of the buds opening during aberrant warm winter weather. These areas of the garden warm up slower than south or western exposures. Northern gardeners who know that they are in it for a long cold spell can wrap their hydrangeas in burlap for winter protection. Planting the shrubs near house foundations also offers some refuge from cold temperatures.
In my Mid-south garden I fertilize my hydrangeas twice during the summer with a slow release fertilizer, usually in June and then again in August. In cooler climates this can be done once, usually in June. Follow the directions indicated on the fertilizer package. Just remember that too much nitrogen will result in an abundance of lovely leaves at the expense of blooms.
Over the years I have broadened my selection of hydranges to include H. paniculata 'Tardiva', H. arborescens 'Annabelle', H. quercifolia (oakleaf), and H. paniculata 'Limelight', but I still treasure the old-fashion varieties for their colorful, long lasting flowers.