Count on Hydrangeas for long-lasting beauty in the landscape. These deciduous, summer-flowering shrubs unfurl blooms in shades of pink, red, lavender, blue, chartreuse and white.
Give plants morning sun with afternoon shade (all-day dappled shade in the South), well-draining soil rich in organic matter, and ample water, and you'll be rewarded with a spectacular flower show.
Changing Flower Color
With Mophead, Lacecap and Panicle Hydrangeas, you can shift blossom color – from blue to pink or vice versa. With other Hydrangeas, flower color is stable, although many white blooms blush pink as they fade.
Flower color depends on whether plants access aluminum in soil, which depends on soil pH. Acid soil (plus aluminum) creates blue-toned blooms, while alkaline soil yields pink. It's easier to shift pink to blue; blue to pink is more difficult. The process of changing color can take about a year.
For blue blooms: Mix 1 tablespoon aluminum sulfate in 1 gallon of water. Apply monthly to 2-3-year-old plants during growing season. Water plants before application. Pour solution on slowly to avoid burning roots. Use low-phosphorus, high-potassium fertilizers; avoid bone meal and superphosphate.
For pink blooms: Add dolomitic lime to soil several times a year to raise pH (no higher than 6.2). Use high-phosphorus fertilizers (similar to 25-10-10; phosphorus is the middle number).
Types of Hydrangeas
Mophead Hydrangea (Hydrangea macrophylla)
Mopheads are the most popular Hydrangea. Plants have large, rounded flower heads. Blossom color is changeable, except for white varieties. USDA zones 4-10, depending on cultivar. For reliable flowering in coldest zones, grow ever-blooming types.
Pruning: Prune to shape shrubs in summer, before August. Plants form buds for next year's blooms in late summer and fall. Remove dead stems or flowers at any time. Prune Everblooming Mopheads (such as Endless Summer) during the dormant season.
Lacecap Hydrangeas have a looser form and fit naturally into woodland settings. Flat flower heads have small, fertile flowers surrounded by large-petaled ones. Blossom color is changeable, except for white varieties. USDA zones 5-10, depending on cultivar.
Pruning: Same as for Mophead Hydrangea.
Oakleaf Hydrangea (Hydrangea quercifolia)
This hydrangea tolerates sandy soils. Flowers are white, blushing pink as they age. Foliage resembles oak leaves; fall color is striking (burgundy, red, orange, yellow). USDA zones 5-10.
Pruning: Same as Mophead Hydrangea.
Smooth Hydrangea (Hydrangea arborescens)
Very large flower heads tend to bow after heavy rain. Support shrubs early in the season by inserting stakes, or plant beside a fence. Annabelle is the most commonly sold variety. USDA zones 3-10.
Pruning: Prune any time, except when flower buds are present. Prune plants to the ground each winter to reduce overall plant size. Or cut stems 12-18 inches tall annually, and they'll thicken over time and support the heavy-headed blooms. Cut to remove dead wood or dead flowers any time.
Panicle Hydrangea (Hydrangea paniculata)
Cone-shaped flowers cover large plants that grow 8-10 feet tall and wide. White blossoms blush pink as they age. This is the only Hydrangea that can be trained into tree form. USDA zones 3-10.
Pruning: Same as for Smooth Hydrangea; annual pruning isn't necessary.