ORNAMENTAL WILLOWS (SALIX SPP.) FOR ALPINE AND SMALL URBAN GARDENS

Journal of Arboriculture, Mar 2004 by Kuzovkina, Yulia A, Quigley, Martin F

Willows benefit significantly from occasional pruning, to prevent unkempt appearance and to stimulate new growth, especially as plants become older. If branches were affected by disease or injured during cold winter, then rigorous pruning into healthy tissue will promote new growth and help to overcome the problem. All species except S. variegala have their flower buds located on branches formed the preceding year, so the best time to prune is in early spring or right after flowering (for precocious species). Because the ultimate size of many willows can be limited by coppicing, some naturally large-growing but ornamentally valuable willows such as S. elaeagnos can be incorporated into the small garden.

Different crown forms, including weeping, contorted, or arching habits, can be achieved by grafting. Several root stocks, such as S. � smithiana, the hybrid of S. caprea and S. viminalis, are compatible with many species of ornamental top-graft stock. The most popular grafted cultivars in the United States are S. caprea 'Kilmarnock' (weeping pussy-willow), and S. integra 'Hakuro-nishiki' (dappled willow). But many other willows having naturally creeping growth can be grafted onto strong-growing upright willows of variable height, usually from 30 to 170 cm (12 to 68 in.) (Marczynski 1998).

The phenology, certain morphological features such as dwarfing, and physiological traits such as fixed growth, appear to be under genetic but not environmental control. Species from high attitudes and latitudes continue to follow seasonal patterns similar to the patterns in their natural regions: late budbreak and blossom time in spring, annual defoliation a few weeks or even months earlier than locally adapted species, and prolonged dormancy, up to 7 months for some species. Most arctic and alpine species develop only one generation of new shoots per year, but a few under favorable conditions can have several flushes of growth (elongation of more than one terminal bud per shoot each year).

PHENOLOGY

Willow phenology is typically as much as 4 to 6 weeks ahead of other woody plants in a given area. They break bud in very early spring, and most willow species bloom and foliate before other woody plants even begin to emerge. Willows often provide the most important early pollen source for bees and other insects. By early summer (early June), many arctic and alpine willows cease all shoot growth; by late summer, leaf senescence has begun; and in SeptemberOctober, they shed foliage.

While the precise timing of phenological development fluctuates from year to year depending on weather conditions, the sequence of the events is consistent. In central Ohio, the first species to leaf out at the end of March are S. brachycarpa, S. crenata, S. glauca, S. refusa, S. serpyllifolia, and S. variegata. At that time, S. caprea, S. rosmarinifolia, and S. � friesiana are in full bloom. Closer to the middle of April, more species break their leaf buds and start flowering: S. helvetica, S. integra, S. repens, S. purpurea, and S. � grahamii. At the end of April, S. alpina, S. arbuscula, S. bicolor, S. helvetica, S. reinii, S. subopposita, S. tarraconensis, and S. � balfourii are in full bloom. At the end of April, the latest species break dormancy (S. coesia, S. lanata, S. lapponum, S. nakamurana, S. pyrenaica, and S. � ambigua). An appropriate planting of species and cultivars in sequence with one another can provide a long blooming time in the spring garden.