Hydrangea

This group consists of hardy and tender shrubs and woody climbers. They are mostly deciduous plants, though a few of the tender species are evergreen. They are natives of the Himalayas, North and South America, and central and eastern Asia. These flowering shrubs have different flower forms - from the large globes of the "mopheads" to the discs of the "lacecaps" to the thick cones of oakleaf and panicle hydrangeas. They come in an array of colors from pure white to brilliant crimson, pale lilac to intense azure. Some varieties produce blossoms with two-toned colors, while some flowers have contrasting eyes, and some may even be speckled or striped with another color. There are two kinds of florets in the flower heads. The sterile or ray florets are male and form the large, colorful sepals on the outside of the flower head. The fertile or perfect florets are small and inconspicuous. They bear the male and female parts and are usually found in the center of the cluster. The flower heads of mophead hydrangeas consist almost entirely of sterile florets. Besides for their lovely flowers, some hydrangeas are valued for their attractive foliage or bark. The sizes of the plants range from dwarf (about 3 ft. high) to large bushes with stems over 10 ft. high. There are also climbing hydrangeas whose aerial rootlets can bring stems up to 80 ft. high. H. aspera subsp. sargentiana (Sargent Hydrangea) is an attractive medium- to large-sized shrub with hairy shoots and large, plush leaves. The large, flat flower heads are produced in mid- to late summer and are bluish with white ray florets. This variety is excellent for a sheltered shrub border or woodland, but needs shade and wind protection. H. 'Ayesha' is a deciduous shrub that has shiny green leaves and flattened, fragrant flower heads consisting of cup-shaped florets, resembling those of the lilac. They are grayish lilac or pink, depending upon the soil, eventually turning a greenish-blue to turquoise color. H. macrophylla 'Altona' is a mophead hydrangea with flower heads growing up to a foot in diameter. This deciduous plant forms a small shrub with large, rose-colored florets. This variety grows best in shade. H. quercifolia (Oakleaf Hydrangea) is a medium-sized, deciduous shrub valued for its splendid autumn colors. The large, deeply lobed leaves resemble those of the Oak, thus the common name. In late summer, conical heads of large, white, sterile florets are produced. H. serratifolia is a tender, climbing hydrangea that grows best against a wall in sun or shade. It has small, leathery leaves and columnar panicles, up to 6 inches long, of creamy colored flowers.

Pot Cultivation

Hydrangeas are rather easy plants to grow. They prefer loamy, well drained, acidic soil (pH 6.5 to 4.5) enriched liberally with organic matter. Most hydrangeas prefer quite a bit of shade, although H. macrophylla and H. serrata will tolerate much more sun, but will still flourish in mottled sun for part of the day. It is important to keep the roots moist and well fed by covering with mulch; this is especially true with those planted near trees. They may also need protection from spring frosts, which can kill the buds. In some species, the flowers change color according to the amount of aluminum and level of acidity in the soil. H. macrophylla will produce blue flowers in acidic soil where more aluminum is present. The lower the pH, the bluer the flowers. In neutral soil, they take up less aluminum and the flowers are pink. On white flowers, only the eye color of the male flowers will change. To produce blue flowers even if your soil is neutral or alkaline, add aluminum sulfate or sulfur to increase acidity. Plants grown in soil with a pH level higher than 7 (alkaline) can also become chlorotic because of a lack of iron and must be treated accordingly. Pruning should be done in late winter or early spring. This consists of cutting off dead flower heads back to the first leaf node that has buds and dead, weak, or crowded stems back to the base.

Propagation

From April to August, cuttings of hydrangeas may be taken. The cuttings should be made from the ends of non-flowering shoots. Each shoot should have two or three pairs of leaves. Remove the bottom pair of leaves and cut the stem just below a joint. Insert them in well-packed sand in a greenhouse propagating case or in a cold frame that is kept closed until they form roots. Shade them from bright light and sprits with water on sunny days. Once they've formed roots, a little air should be allowed into the frame or glass case. A few days after, the little plants can be potted individually in small containers filled with equal parts of peat, leaf mold, sandy, lime-free loam and coarse grit.