Hydrangeas have been popular garden plants for decades. Older varieties add sentimental charm and new hydrangea shrubs can bloom from mid-summer through fall. Hydrangea flowers now come in an even wider variety of colors, including bright blue, deep red, and pale green. These versatile shrubs will thrive in both sandy coastal soils and in shady woodland sites and almost everything in-between.
To ensure hydrangea shrubs have time to establish a healthy root system before blooming, it is best to plant them in the fall or early spring at the latest. Once planted, hydrangeas are rapid growers averaging 24 or more inches of growth per year.
|Botanical Name||Hydrangea spp. (including H. macrophylla, H. serrata, and others)|
|Mature Size||Up to 15 feet|
|Sun Exposure||Full sun to partial shade|
|Bloom Time||Mid-summer through fall|
|Flower Color||White, blue, green, red, pink, purple|
|Hardiness Zones||5 to 9|
|Native Area||Asia and the Americas|
How to Grow Hydrangeas
The most commonly grown hydrangeas used to be the bigleaf hydrangeas (Hydrangea macrophylla) and mountain hydrangeas (Hydrangea serrata). Both are deciduous shrubs, native to seacoasts and mountain valleys in Japan, and they are categorized by the shape of their flowers. Mopheads (sometimes called hortensias) have large, round flower clusters; in contrast, lacecaps bloom in flat, delicate clusters.
Most hydrangeas adapt to a wide range of growing conditions. They are hardy from USDA hardiness zones 5 to 9. As long as they are planted in well-draining soil with plenty of organic matter, they should grow well.
Too much shade can reduce hydrangeas' flower output. Hydrangeas do well in the partial shade provided by tall deciduous trees, especially if they receive morning sun and the partial shade is in the heat of the afternoon. They will also thrive in full sun but may need extra water on hot summer days (bigleaf hydrangeas do particularly well in full sun in coastal areas once they are established).
One of the perks of growing hydrangeas is being able to change their color. Although somewhat determined by cultivar, color can be changed or "tweaked" by the amount of aluminum in the soil and the soil pH. The soil pH determines how available aluminum is to the plant. Acidic soil (aluminum available to the plants) will give you blue flowers, and alkaline soil (aluminum unavailable to the plants) will give you pink flowers.
To decrease the acidity of your soil and change flowers from blue to pink, add hydrated lime to your soil in the spring. To increase the acidity of the soil (to change flowers from pink to blue), add aluminum sulfate to your soil in the spring or mulch with oak-leaf mulch.
Regular water is vital for healthy plants. Hydrangeas benefit from one inch of water a week during summer (unless it rains). Bigleaf hydrangeas in full sun may need up to two inches during the hottest summer days.
Temperature and Humidity
In areas with bitterly cold winters, dieback, a plant dying from the tips of its leaves inward, can be a problem. Protect your hydrangeas from cold winds by planting them in a sheltered spot or with a burlap windscreen or a burlap frame filled with dry leaves. It may sound counter-intuitive, but a north- or east-facing site, where temperatures remain somewhat constant is a better choice than a spot on the south and west side of your property, which will heat up in the winter sun and may cause hydrangea buds to open prematurely, leaving them vulnerable to cold snaps.
If hydrangeas are given too much high-nitrogen fertilizer, they may grow full and lush, but there will be fewer flowers. If the soil is rich, fertilizer is not needed. Otherwise, a light application in March or April may be warranted.
Varieties of Hydrangea
There are two main groups of hydrangeas: plants that bloom on new growth (the current year's stems) and those that bloom on old growth (last year's stems).
New-growth hydrangeas include smooth hydrangea (Hydrangea arborescens) and Panicle hydrangeas (Hydrangea paniculata). These shrub-size plants come in a range of colors. Some popular varieties of smooth hydrangea are 'Annabelle', 'Grandiflora', and White Dome. Panicle hydrangea cultivars include 'Burgundy Lace', 'Chantilly Lace', 'Grandiflora', 'Limelight', 'Little Lamb', 'Pee Wee', and the late-flowering 'Tardiva'.
Old-growth hydrangeas include bigleaf hydrangeas, mountain hydrangeas, and oak-leaf hydrangea (Hydrangea quercifolia). These varieties are hardy down to USDA zone 4 and flower for extended periods. Oak-leaf hydrangea, which boasts an intense red fall color, is a low-maintenance shrub that needs little pruning and thrives in partial shade. Some cultivars to look for are 'Alice', 'Amethyst', 'Snow Flake', and 'Snow Queen'. Mountain hydrangea will also flower over a long period. Good cultivars of these include 'Beni-gaku', 'Geisha Girl', 'Kiyosumisawa', 'Miranda', 'Miyama-yae-murasaki', 'Tiara', 'Woodlander', and 'Yae-no-amacha'.
If caring for old-fashioned hydrangeas sounds too complicated, choose ever-blooming hydrangeas because they flower almost continuously throughout the season. Cultivars include Hydrangea macrophylla 'All Summer Beauty', 'David Ramsey', 'Decatur Blue', Endless Summer, Mini Penny, 'Oak Hill', and 'Penny Mac' Hydrangea serrata 'Blue Deckle', and 'Coerulea Lace'.
Although not quite as continuously blooming as the ever-bloomers, free-flowering hydrangeas flower over an extended season. The free-flowering hydrangeas include Hydrangea macrophylla 'Altona', 'Ami Pasquier', 'Europa', 'Forever Pink', 'Frillibet', 'General Vicomtesse de Vibraye', 'Lilacina', 'Lanarth White', 'Madame Emile Mouillere', 'Mousseline', 'Nikko Blue', and Hydrangea serrata 'Fuji Waterfall'.
Hydrangeas need minimal pruning, but if you would like to reduce the size of the plant or prevent it from flopping over too much after the flowers fade you can remove some of the older canes, which will reduce crowding and encourage new growth.
The exception to this rule is when cold winters kill the tips of the branches. Then you should prune in the spring, removing the dead wood and cutting the stems back to a healthy set of buds. If you have an established shrub, you can also take out several of the older stems at this time. Just don't remove all the buds; otherwise, you will lose your blooms.