Hydrangeas: A Color Changing Flowering Bush
Hydrangeas are among the most popular of plants. Their huge midsummer flowers can almost stop traffic, but may be tricky to grow. However, with careful selection, virtually all gardeners can enjoy hydrangeas.
When choosing a plant, note the type of hydrangea. Big leaf hydrangeas (Hydrangea macrophylla) have large colorful flowers and are very popular even though they are the least hardy type. The blooms often fail because of a hard winter, an untimely frost or inappropriate pruning.
Hydrangeas produce beautiful flowers from mid-summer through fall. These classic garden flowers fit into almost any garden. Use a mass planting as a dramatic hedge, or incorporate them into existing perennial beds. Many varieties are good for cutting and drying, providing enjoyment year-round. If you’ve been afraid to try hydrangeas because they seem complicated, don’t be. Just ask at your local garden center for a variety that’s suited to your area. Wherever you garden, there’s a hydrangea for you.
5 Different Types of Hydrangeas
The most common and familiar Hydrangea is the Hydrangea macrophylla, more commonly called Garden Hydrangea or French Hydrangea. This plant is popular not only for it’s huge bounties of flowers, but also because the color of its flowers can actually be changed from pink or red to white or bright blue, all with simple adjustments to the soil pH and aluminum content. Because Garden Hydrangea produces buds in the autumn and flowers in the spring, care must generally be taken to protect those buds from freezes in early fall and late spring. However, in recent years several cultivars have been developed which can produce buds on new wood in the spring, meaning that these new varieties can still flower even if the cold kills the buds.
The most cold-hardy specie of Hydrangea is the Panicle Hydrangea, Hydrangea paniculata. Because these Asian natives are the largest type, growing as tall as fifteen feet, they are often pruned into tree form, and are sometimes sold as “Hydrangea trees.” Panicle Hydrangea bloom in mid-summer with large white flowers on six- to eighteen-inch panicles. The flowers of Panicle Hydrangea often mature to a light pink color. Most panicle hydrangeas have white flowers, but newer varieties have more colors. ‘Limelight’ has large soft green flowers that turn pink each fall. Limelight grows in sun or partial shade. Winner of the prestigious Pennsylvania Horticultural Society Gold Medal, Limelight is a great addition to existing shrub borders, or planted en masse as a low-maintenance hedge. The flowers are perfect for cutting and will retain some green color when dried.
The larger of the two Hydrangea species native to the United States is the Oakleaf Hydrangea, Hydrangea quercifolia(H. arborescens being the only other native of which I am aware).
Oakleaf Hydrangea produce four- to twelve-inch panicles of large white blooms in early summer. Like the Panicles, these blooms often mature to a pink or rose color. The Oakleafs are best known, though, for their beautiful foliage, which color in fall to a lovely, deep bronze. It is the only Hydrangea that produces significant fall color. It blooms best in areas where summers are somewhat hot, but it is winter hardy farther north than the macrophylla (mophead). A tremendous advantage of the Oakleaf is that it can thrive in much dryer locations than its cousins.
The other native specie is the Smooth Hydrangea, Hydrangea arborascens(H. arborescens), commonly called “Annabelle”. Annabelle is the best known variety of Hydrangea arborescens. Until recently, this is the only arborescens variety easy to find in garden centers or even recognized by the public. It appears naturally from New York all the way to Florida and Louisiana. Smooth Hydrangea are nearly as cold-hardy as the Hydrangea paniculata, but they can survive much warmer areas (all the way to zone 9). These shrubs only grow to about five feet in height, and they are often used in mass plantings, where the white midsummer blooms have the most striking effect. The blooms of the Smooth Hydrangea mature to a lovely pale green.
The most unusual specie is the Climbing Hydrangea, Hydrangea anomala. It is the slowest to bloom of the common Hydrangea, producing white lacecap inflorescences in early or midsummer on established plants. However, Climbing Hydrangea is quickly becoming one of the most sought-after species of the genus in America because it is a true clinging vine. Hydrangea anomala, commonly known as climbing hydrangea, is a vigorous, sprawling, deciduous, woody vine that clings and climbs by twining and aerial rootlets along the stems, typically maturing over time to 30-40’ long. Horizontal lateral branching often extends several feet beyond supporting structures. It has been known to cover structures as large as eighty feet tall, and when it is in full bloom the effect is nothing short of spectacular. Unsupported vines sometimes will grow in the form of a mounding shrub to 3-4’ tall, sprawling along the ground like a ground cover eventually covering an area of up to 200 square feet. This plant is native to wooded valleys, stream banks and mountain slopes in the Himalayas and China.
Know your USDA Hardiness Zone
General Hydrangea Care
Planting your hydrangeas in early spring or in the fall is ideal. If you plant them in the summer, they need a lot more water in the beginning to establish the root system. Most varieties thrive in full sun to part shade, as long as they are planted in moist, rich soil. Water deeply once a week, and maybe more, if the weather is particularly hot or dry. Hydrangea fertilization needs vary greatly, depending on your intended bloom color. Certain elements of the fertilizer affect the soil pH, which is a major determinant of bloom color in the pink/blue hydrangea varieties.
How to Adjust Hydrangea Color
Odd as it sounds, a particular hydrangea may produce pink, blue, or lavender blooms, depending on where it’s planted and how it’s fed. The presence of aluminum in the plant ultimately determines the color, and pH affects the uptake of aluminum. Alkaline soils, pH of 6.0 or more, are more likely to produce pink blooms, and more acidic soils, pH 4.5 to 5.5, produce blue flowers. Pink hydrangeas can be turned blue by applying aluminum sulfate to lower the pH level and add aluminum to the soil. Applying lime to raise the pH level will help blue hydrangeas turn pink. If your soil naturally produces very blue or very pink hydrangea flowers, you may need to grow your hydrangeas in containers or raised beds to achieve the desired color without battling nature. If you do attempt to change the color of your blooms by adding these minerals, dilute them well, and add sparingly. It is very easy to scorch your plants by adding too much. By the way, white hydrangeas are not affected by efforts to change bloom color.
Learn how to test your soil PH here
Some people never prune their hydrangeas, but this often leaves gangly plants with dead stalks hanging out all over. Most varieties of hydrangeas respond beautifully to well-timed pruning. It is always OK to remove dead or unhealthy stalks–this makes your plant look better and allows it to focus its energy on growing and flowering. Early spring is generally the best time for pruning–if your plant is out of control, it may be due for a severe pruning, allowing room for new, healthy growth.