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New crop of hybrid plants demonstrate beauty of ingenuity

By Joel M. Lerner
Friday, January 28, 2011; 11:10 AM

Numerous newly hybridized plants are introduced every year with the goal of creating trees, shrubs and perennials that perform well, are hardy, pest-resistant and long-lived and that display practical and aesthetically pleasing characteristics. Here are some introductions that I'm fond of.

lFirst lady flowering cherry (Prunus X incam 'Okame') crossed with (P. campanulata) is a perfect example of a successful plant-breeding project and of the lengthy period required for development before a plant is introduced to the public. Bred at the U.S. National Arboretum in 1982 by Donald Egolf, first lady flowering cherry was developed for flower color and hardiness. One seedling proved to be outstanding, with deep rose-colored, almost red flowers, good cold hardiness and a distinctly upright growth habit. This small flowering cherry - which grows to 27 feet tall by 14 feet wide in 20 years - was named first lady in 1988, officially released in 2003 and registered with the International Registration Authority for Unassigned Woody Genera in 2004. This tree took about 22 years from first breeding to its introduction to the public.

lGreen giant arborvitae (Thuja standishii X plicata 'Green Giant') is an effective screen for property lines and dividing large properties into room-size spaces. Green giant has a tightly pyramidal to conical habit branching full to the ground, is evergreen with rich green color and grows vigorously.It is an outstanding plant in the Washington region. It has been widely grown and tested in commercial nursery production and has no serious pest or disease problems. It is an excellent substitute for Leyland cypress, growing to 30 feet tall in 30 years and eventually reaching as high as 60 feet, with a 12 to 20 foot spread. It is adaptable and grows in soil types from sandy loams to heavy clays, requiring little to no pruning.

lConoy viburnum is a selection from the cross of V. utile with V. X burkwoodii 'Park Farm Hybrid' bred in 1968 by Egolf at the National Arboretum. Selected for field trial and propagation in 1976, Conoy was named and released in 1988. It is distinguished from other burkwood viburnum cultivars because of its compact spreading growth habit - four to five feet tall and seven to eight feet wide. It has fine-textured, densely-branched, evergreen foliage and persistent, abundant, glossy red fruit lasting about six to eight weeks in the fall. Its dark pink buds produce many creamy-white flowers in spring, and the foliage has a maroon hue in winter. Grown best in full sun to partial shade in heavy loam with adequate moisture, it tolerates drought and dry soils well. Use it as a specimen plant as a natural or sheared hedge, foundation plant or massed grouping. It also can be grown in containers.

lKnock Out roses are one of the most disease-resistant roses on the market, are easy to grow, do not require special care and have stunning flowers. Their generous bloom cycle - about every five to six weeks - continues until the first hard frost. Spent blooms do not require deadheading. Plants are winter-hardy and heat-tolerant throughout most of the United States. If unpruned, the Knock Out can easily grow to more than three or four feet tall and wide. Periodic trims will keep them as a smaller plant. A once-a-year cut (to about 12 to 18 inches above the ground) in early spring after the last hard frost is recommended for maximum performance. Knock Outs can fit into any landscape. Plant them individually among shrubs, annuals and perennials in mixed beds and borders or in large groups to create colorful hedges or along a foundation for a bright border.

lCallicarpa dichotoma 'Duet' is an excellent edge-of-woods plant. Gary Bachman and W. Edgar Davis discovered a variegated sport of callicarpa dichotoma 'Albifructus' at Tennessee Technological University in 2000. The National Arboretum and Tennessee Technological University released duet jointly in 2006. Duet is the first dependably variegated beautyberry, selected for its yellow-margined, variegated foliage and tolerance to full sun. This deciduous, rounded shrub grows about 61/2 feet high and wide in four years, producing white fruit in September that persists for one to two weeks after leaves drop. This white-flowering member of the verbena family has handsome, shiny leaves. Duet can be grown in full sun in USDA hardiness Zone 7 and cooler zones without the yellow margins of the leaves burning, but it may benefit from light shade in warmer climates. Leaves become sparse in heavy shade. Its disease- and insect-tolerant foliage make it an ideal plant for a low-maintenance landscape.

lPocomoke crapemyrtle (Lagerstroemia indica X fauriei 'Pocomoke') is a dwarf crapemyrtle hardy to Zone 7. Pocomoke was produced and selected at the National Arboretum by Egolf from five original plants and their progeny that were intercrossed for five generations. The first cross in this pedigree was made in 1967 and the final cross that resulted in Pocomoke was made in 1989. The plant was released for sale in July 1998 -31 years after its first cross. Pocomoke is the second in a series of true miniature hybrids, reaching a height of 19 inches and a width of 35 inches after eight years. This deciduous, densely branched, compact shrub is highly tolerant to powdery mildew, has small, glossy, dark green foliage in spring and maroon to bronze-red fall color. It flowers in mid- to late summer with rose pink flowers that persist until frost, and it grows best in full sun and in heavy loam with a pH of 5.0-6.5. It makes a good small foundation, accent or container plant on patios. I consider this to be an underused plant in the landscape.

lSparkleberry holly, a cross between Ilex serrata and I. verticillata, is a large deciduous shrub with a striking and long-lasting display of brilliant red winter berries. Planted in a massed grouping, sparkleberry will add brilliant color to the winter landscape. It is a female selection and requires a pollinator for good fruiting. Apollo, a male selection of the same cross, is the recommended pollinator to produce the showiest berries on the female. It will grow 12 feet high and wide and thrives in wet or dry soil. Sparkleberry holly tolerates air pollution and salts and adapts to a wide range of soil types.

lOne of my favorite native ornamental grasses is blue switchgrass (Panicum virgatum). It is an excellent ground cover as a meadow-style planting or standing among other flowering perennials in a border of shrubs and flowers. Used as an accent in your garden, switchgrass is a good plant to use because it holds architectural interest well into winter and fits in with most mixed perennial gardens. It is difficult to choose a favorite hybrid. Switchgrasses are all so different, each with its own habit. All are sturdy plants that make excellent focal points in the winter garden. Hardy to Zone 4.

l Virginia sweetspire (Itea virginica), an arching deciduous shrub, spreads by rhizomes. It forms colonies with fragrant, creamy white flowers in late spring and has maroon fall foliage. It has never disappointed me in wet or dry conditions and will colonize well. My favorite hybrids are Henry's garnet, growing to six feet, and little Henry, which grows to three or four feet. The species grows too large to fit most gardens, reaching 10 feet in maturity.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md.

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