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Choice"This resource would prove useful both to casual gardeners and serious botanists."—R. L. Krajewski, Choice, February 2005
— R. L. Krajewski
In general, hydrangeas are easy to root, and cuttings with two pairs of buds give the best results. The pair at the bottom of the cutting is inserted in the rooting medium, while the higher pair with two leaves is left exposed. If the leaves are large, they should be pruned to half the blade. This practice helps to decrease the respiration of the cuttings.
Single cuttings are usually inserted in 7-cm (ca. 3-inch) pots or in trays with prefabricated little pots. Well-rooted cuttings can be potted in 3-liter (ca. 0.5 gallon) pots in March, and these usually grow into plants with two to three branches and few flowers. For a good display of flowers, the cuttings need to grow another year. Weak cuttings are potted in 9-cm (ca. 4-inch) pots and left in the frame or greenhouse. It is possible to start cuttings in the open field instead of pots, again depending on the climate. In the middle of the 20th century almost all hydrangeas for garden use were grown in the open field. It was only toward the end of the century that pot-grown plants took over.
Professional growers of potted hydrangeas use a more complicated method, pruning the plants mechanically or chemically in various stages of their development, cooling them in slightly refrigerated warehouses to make sure that the plants will develop at least three to five flowers and remain reasonably compact. These treatments are necessary to ensure a crop that flowers reliably on a predictable date in a predictable fashion, but they are not necessary to ensure good and healthy plants. On the contrary, plants treated in this manner, especially those grown indoors, have a more difficult time becoming established in the garden than those grown in the old-fashioned way outdoors. Yet, the retail market demands a visually attractive product that can easily lure consumers into buying a hortensia, so growers choose to grow plants indoors even though the average gardener is better served by an outdoor-grown nonflowering plant.
Growing potted hydrangeas by the newer, more complicated method limits the number of cultivars that can be grown. Few plants respond well to such treatment, especially among cultivars of Hydrangea macrophylla. Many cultivars do not reliably produce enough flowers when young, so commercial growers ignore the beautiful ones among them to satisfy their customers' needs for flowering plants.
In addition to softwood cuttings, gardeners use other methods to propagate hydrangeas. Layering gives plants of good quality, but only in very limited quantities. Some hydrangea cultivars root from hardwood cuttings, taken in December or January and grown in a greenhouse. Unfortunately, this method produces unreliable results, so few professional growers use it. Finally, it is possible to grow plants from seed. These seedlings are very variable and not suitable for commercial purpose, except maybe in the case of wild-collected seeds from rare species. Seedlings, especially from seed of garden origin, can produce novelties, but careful selection and trials are essential, as there are so many beautiful named cultivars already.