Hybrid willows are crosses between two or more different willow species or cultivars. These crosses are referred to as hybrid willows and tend to be more vigorous than their parents. Hybrid willows will exhibit traits of the different parents and is a way for plant breeders to introduce something like variegated leaves or fast growth to a weeping form. It takes years of experimentation and testing—the growth rate, hardiness and growing requirements are tested—before a willow hybrid is available for sale.
Hybridization is the process of crossing two plants from different species, varieties or genera. Hybrid plants tend to be hardier than their parents, grow faster, and have larger flowers and fruit. This trait is called hybrid vigor. Hybrid vigor doesn't necessarily mean that hybrid willows are better than species, or nonhybrid, willows but it does give them some advantages. Hybrid willows are more tolerant of temperature extremes, have fewer insect pest and disease problems, and grow faster and taller than species willows.
Willows were first hybridized in Germany in the late 1880s. One of the first hybridized willows, called Golden Weeping Willow, is still available to gardeners.
The modern hybridized willow was originally developed for bio-energy production until researchers realized that this extremely fast-growing hybrid willow makes an excellent wind and privacy screen.
When you see plant catalogs advertising fast-growing hybrid willows for erosion control, windbreaks and privacy screens, you are looking at a hybrid of Salix alba, or white willow. There are several Salix alba crosses available to gardeners, although all are sold under the name hybrid willow. These hybrids are extremely fast-growing, often growing 6 to 10 feet a year. The fastest growth occurs in the first five years after planting, with the plant reaching maturity between five and seven years. These willow hybrids are suited for hedges, windbreaks or privacy screens because they have close-growing branches that start at the base of the plant and an upright growth habit. You can turn one of these crosses into a specimen tree; however, they typically don't have the graceful arching branches of species willows.
The other types of willow hybrid most commonly available are weeping-form descendants of species weeping willows. These trees have the arching branches of their parents and make excellent specimen trees.
Hybrid willows are hardy in all states, reach a mature height of 35 to 75 feet depending on variety, and can live 20 to 40 years with proper care.
All willows, including willow hybrids, prefer to be planted in moist to wet soil. This doesn't mean you can't plant willow hybrids in dry soil; you will just need to mulch under the tree with 2 to 3 inches of organic mulch and provide water during dry months. Hybrid willows tolerate all soil types and are a good choice for clay soils.
Site your hybrid willows where they will receive full to part sun. For a windbreak or privacy screen, space your willows 3 to 4 feet apart. Fertilize your hybrid willows in early spring, and again in early summer to midsummer, with compost or a commercial 10-10-10 fertilizer. Hybrid willows need to be pruned to remove dead or dying branches.
To plant your hybrid willows, dig a hole twice as wide and twice as deep as the root ball. Mix the soil you removed from the hole with compost or well-rotted manure. Refill the hole until it is just deep and wide enough for the root ball. Place the hybrid willow in the hole and cover the roots, firmly tamping down the soil to eliminate air pockets. Because hybrid willows grow so quickly, providing compost in the hole gives them the nutrients needed for optimum root and plant growth.
Hybrid willows may become invasive in some areas. Willows are dioecious, meaning plants are either male or female. Hybrid willows are sold as sterile males; however, some hybrid willows turn out to be fertile males and can cross with species willows, forming new hybrids. These new hybrids are spread into new areas, making them invasive noxious weeds. If your hybrid willow forms catkins, you have a fertile male tree.
Some hybrid willows will produce suckers, with the suckers producing more suckers, until the original hybrid willow eventually forms a thicket if not pruned.
Due to the fast growth of hybrid willows they can often have problems with weak crotches, the point where the branch attaches to the trunk. High winds or ice can cause branches to break, posing hazards to homes and overhead wires.
- Hybrid Salix
- The Garden Primer; Barbara Damrosch; 1988
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