Hydrangea
(from hydor, water, and aggeion, a vessel; in allusion to the cup-shaped fruit). SYN. Hortensia. ORD. Saxifrageae. A genus consisting of thirty-three species of greenhouse or hardy, deciduous or evergreen, showy shrubs or trees, natives of Eastern Asia, Java, the Himalayan Mountains, North-west and South-east America. Petals four or five; calyx superior, five-toothed; stamens eight to ten; capsule membranaceous. Leaves opposite, petiolate, persistent or deciduous, entire, serrate, or lobed. Hydrangeas are of easy culture, and are exceedingly ornamental for conservatory, room, or window decoration. They are also well adapted for growing in the open ground, in all the warmer parts of the country. The sorts having abortive or sterile flowers, with an enlarged calyx, are the most ornamental, and are extensively grown. H. hortensis, and some of its varieties, have nearly all sterile flowers, and are, consequently, most popular. H. paniculata grandiflora is very handsome, and amongst the best, either for pot culture or for outside treatement. The American species are hardier, but not so ornamental, as those from China and Japan. Propagation is readily effected from cuttings of young or partially-ripened shoots, which may be inserted at almost any time when they are procurable. Old plants may also be divided for propagation. For culture outside, a somewhat sheltered position should be selected, except in favourable localities.
Cultivation in Pots. Hydrangeas may be propagated annually to produce one head of flowers each--a method largely practised--or they may be grown as shrubby plants several years in succession. Cuttings should be inserted in small single pots, and plunged in a close, warm frame. They may be taken in spring, from young growths that are not bearing flowers, and be grown on throughout the summer, and well ripened in autumn by exposure outside. Another plan is to let the old plants grow all the season, and put in strong points as cuttings when partially ripened. In this case, the formation of roots only should be encouraged, by plunging in a little bottom heat, but not in an inclosed frame. Select the tops of the strongest and most prominent shoots for cuttings, and insert them in August. When they are rooted, gradually harden off, and expose them to full sunshine and plenty of air in autumn, to insure through ripening. When the leaves fade, water should be withheld, and the plants kept dry, in a cool greenhouse, all the winter. In February, or earlier if desired, they may be potted into 5in. or 6in. pots, and started by placing in a higher temperature, and applying more water. The embryo buds, formed the previous autumn, will soon begin to expand; but it is not usual for all to flower, as they may not have been sufficiently strong. As a rule, the corymb of flowers appears after the fourth pair of leaves; and should the plant develop so far without the embryo being seen, it may be thrown away, unless required for another year. Late autumnstruck cuttings produce useful dwarf-flowering plants in spring, not exceeding 1ft. in height. Those propagated in spring, and grown on in pots for the next year, are much stronger and taller in proportion. A new stock should be propagated annually, and the old ones thrown away, unless required for bush specimens or for supplying cuttings, when they may be cut down, repotted, and grown on in pots, or be planted out in the open air. Hydrangeas like a rich soil, such as loam and decayed cow or other manure in equal parts. Any quantity of water may be applied in the growing season; and artificial manure, given just as the flowers are developing, invariably proves beneficial. The flowers sometimes turn blue, certain soils having the property of changing the normal colour, in consequence of the presence of some chemical constituent. Water, in which alum has been dissolved, is used artificially to cause the same change in colour. Iron in small quantity, as well as some other substances, mixed with the soil, are said to produce the same effect. In some gardens, plants that produce red flowers one year may develop blue ones the next, and this without any influence or skill on the part of the cultivator. H. arborescens (tree-like). fl. white, small, having an agreeable odour, nearly all fertile; corymbs flattish. Summer. l. ovate, rather cordate; upper ones lanceolate, coarsely toothed, pale and puberulous beneath. h. 4ft. to 6ft. North America, 1736. Hardy. (B. M. 437.) H. hortensis (garden).* Common Hydrangea. fl. varying much in colour (according to the soil in which the plant is grown), disposed in ample corymbs or cymes, all difformed; fertile flowers few. April to September. l. broadly-ovate, serrated, acuminated. h. 2ft. to 3ft. China, 1790. SYN. Hortensia opuloides. The varieties of this species are numerous; one of the most noteworthy being "Thomas Hogg," a form with pure white flowers. H. h. japonica (Japanese). fl. blue, white, difformed; cymes crowded. l. ovate-oblong, acuminated, finely and glandularly serrated, glabrous. h. 3ft. Japan, 1843. The variety roseo-alba has the outer flowers only radiate, and either white or rosy toothed petals; and caerulescens has bright blue ray-flowers. There are also forms having leaves with gold and silver variegation.
H. h. Otaksa (Otaksa).* fl. flesh-coloured, nearly all sterile, disposed in large, terminal, globose, leafless cymes. l. opposite, cuneate-obovate, deeply serrated. h. 2 1/2ft. Japan, 1868. Hardy.
H. h. stellata prolifera (proliferous star-like). fl. at first yellowish-green, ultimately rose-colour, sterile; cyme terminal, densely packed. Japan, 1868.
H. h. variegata (variegated) is a variety with very ornamental foliage, particularly when grown as young plants, in heat.
H. paniculata grandiflora (large-flowered panicled).* fl. white, disposed in a large, terminal, leafy panicle, 1ft. long, consisting of openly-arranged, small, star-shaped flowers, intermixed through out with sterile ones, more than 1in. across. Summer and autumn. l. opposite, or in threes, ovate-oblong, acute, pubescent. Japan, 1874. Hardy.
H. petiolaris (petiolar).* fl. white, in flat-topped cymes, 8in. to 10in. in diameter; fertile flowers greenish, very numerous; stamens fifteen to twenty. April and May. l. broadly ovatecordate, acuminate, finely serrate, dark green above, paler beneath; stalk pubescent, and nerves bearded in axils. Trunk slender, branching, rooting like Ivy against its support. Japan, 1876. Cool conservatory. (B. M. 6788.) Now and then met with in gardens under the name of Schizophragma hydrangeoides, a very different plant. H. quercifolia (Oak-leaved).* fl. white, sterile, or outer ones large; corymbs rather panicled, flattish. Summer. l. large, ovate, sinuately lobed and toothed, pilose beneath. h. 4ft. to 6ft. Florida, 1803. Half-hardy or greenhouse. (B. M. 975.) H. scandens (climbing). fl. white; petals cohering at their tips and falling together. Japan, 1879. Plant climbing, half-hardy.
H. Thunbergii (Thunberg's).* fl. blue or rose; the sterile ones on the circumference, and fertile ones in the centre, of the cyme; cymes terminal, 3in. to 4in. in diameter. l. opposite, petiolate, ovate-oblong, acute, serrulate. h. 2ft. to 3ft. Japan, 1874. Half-hardy. (G. C. 1870, 1699.)