Hamilton County Master Gardener Ann Bartlett provides a history lesson on our native show stopper, the hydrangea.
One of the loveliest summer-blooming landscape plants is the hydrangea. The genus contains at least eighty species of deciduous and evergreen shrubs. They are found in the woodlands of East Asia and in North and South America. Let’s look at the five family members available in the nursery trade.
Hydrangea macrophylla, bigleaf hydrangea, is the best known of the tribe. It has the classic almost round flower heads, which many call “mopheads,” composed of sterile florets. A subgroup of this species has “lacecap” flowers. These are flattened with larger sterile flowers encircling very small fertile flowers. Flower color may be influenced by the availability of aluminum ions. If soil pH is greater than six, the flowers are pink. If pH is lower than six, they are blue. White flowering cultivars are unaffected by pH.
Mophead hydrangeas like humus-rich, moist but well drained soil. They tolerate partial shade as well as full sun. These reblooming shrubs flower on last year’s stems. To prune, remove last year’s flower heads to the first bud beneath each flower. If the plant is well established, cut back one fourth to one third of the oldest flower shoots to the base of the plant in early- to mid-spring. Some recent introductions flower on new wood as well as the old. Endless Summer is such a selection.
Hydrangea paniculata, hardy hydrangea, has conical flowers composed of fertile florets. This native of Japan and China has become quite popular. Limelight and Little Lime are two varieties we often see in our area. These flower on new wood. In spring, prune back the previous season’s shoots to a few bud eyes on the woody frame to encourage new growth.
Hydrangea serrata, mountain hydrangea, is native to the mountains of Korea and Japan. This rebloomer prefers a cooler site and tolerates full shade. The flowers are the lace-cap form. Color may be influenced by soil pH. I have seen them for sale in garden catalogs.
Hydrangea quercifolia, oakleaf hydrangea is native to the Southeastern United States. It is valued for providing year-round interest in the garden. The conical flower heads are composed of sterile florets. In autumn the foliage changes color, becoming rust red. The peeling bark is a striking feature after the leaves fall.
Hydrangea arborenscens, smooth hydrangea is another native of the eastern part of our nation. It is found from New York to Florida and as far west as Oklahoma. It likes fertile soil and tolerates light shade. The dome-shaped flowers of the cultivar “Incrediball” are green in the spring, changing to white and then aging to green again. The flowers are useful in dried arrangements. This is another species that blooms on new wood.
Hydrangeas are among the most beautiful blooming shrubs. For a bit of pruning in the spring, the gardener is rewarded with months of spectacular flowers. One last tip: When pruning wear gloves, long pants and shoes with socks. The sap can be quite irritating to the skin.
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