Hydrangeas (Hydrangea spp.) bloom in spring and summer, with exact bloom times varying by species. Some species bloom longer than others, and certain cultivars can bloom more than once in a growing season. For hydrangeas, blooming is directly related to when you should prune plants, and improper pruning can prevent hydrangeas from blooming at all. Some species flower on old wood and should be pruned right after flowering, while others flower on new wood and should be pruned in the fall, winter or early spring.
Also called hortensia hydrangea or lace cap hydrangea, depending on the bloom style, bigleaf hydrangea (Hydrangea macrophylla) is the most common garden hydrangea. Bigleaf hydrangea grows best in well-drained soil in locations with morning sun and afternoon shade. It is hardy in U.S. Department of Agriculture plant hardiness zones 6 through 9.
Bigleaf hydrangea blooms in the spring and early summer with blue or pink flowers. The hortensia or mophead varieties have large, ball-shaped flower heads, while the lace cap hydrangeas display a loose and open flower head. Most varieties bloom on old-growth, meaning that next year's flowers will appear on the growth made after flowering. If you want to prune these bushes, do so immediately after flowering to avoid removing next year's blooms.
A few bigleaf hydrangea cultivars are reblooming, and flower once in the summer and again in the fall. In the summer, these cultivars bloom on old wood from last year, and then they bloom again on new growth in the fall. One example is Endless Summer hydrangea (Hydrangea macrophylla 'Bailmer'), which is hardy in USDA zones 4 through 9. If you prune this plant, prune in summer after the blooming.
Oakleaf hydrangea (Hydrangea quercifolia) is hardy in USDA zones 5 through 9. It is well-suited to shaded locations, though some cultivars tolerate more sunlight than others. The plants grow and bloom best in well-drained, fertile soil.
This hydrangea blooms in the summer and is not reblooming. They have large, cone-shaped flowers that start out green, turn white in the summer and then fade to a purplish pink in mid- or late summer. Some cultivars, like Snowflake oakleaf hydrangea (Hydrangea quercifolia 'Snowflake') have double blooms. This cultivar is hardy in USDA zones 5 through 9.
The flower buds are produced on old wood, so prune oakleaf hydrangea right after flowering to avoid damaging next years flowers. Oakleaf hydrangea also provides fall interest with brightly colored fall foliage, and winter interest from exfoliating bark on twisted stems.
One of the most reliable hydrangeas, smooth hydrangea (Hydrangea arborescens) is long-lived and spreads from underground stems. This plant grows well in partial sun or light shade and, like other hydrangeas, prefers moist well-drained soil. Smooth hydrangea is hardy in USDA zones 3 through 9.
This hydrangea blooms in midsummer, with flowers that start out green and turn white. The cultivar 'Annabelle' (Hydrangea arborescens 'Annabelle') is an exceptionally prolific bloomer, and produces large white flowers all summer long. Like the species variety, it is hardy in USDA zones 3 through 9.
Smooth hydrangea blooms on new growth that is produced in the spring, so you can prune them in the fall, winter or very early spring. You can cut the plants all the way down to the ground, but after a few years this results in weak growth. It's best to only prune when removing weak or dead stems.
The hydrangea best suited for bright sunlight, panicle hydrangea (Hydrangea paniculata) can grow in full-sun conditions if the well-drained soil has enough moisture. In locations that are dryer, make sure it gets afternoon sun. It is hardy in USDA zones 3 thorough 8.
Panicle hydrangea blooms in midsummer with white blooms that stay on the plant and turn pink in the fall. Most cultivars have cone-shaped flowers, including the well-known Pee Gee hydrangea (Hydrangea paniculata 'Grandiflora'), which is hardy in USDA zones 3 through 8.
Like smooth hydrangea, planicle hydrangea blooms on new growth and can be pruned in the fall, winter or early spring. It doesn't require yearly pruning, and removing dead stems is usually all the maintenance required.