Flowering shrubs

When it comes to choosing flowering shrubs, it's tempting to stick with a handful of tried and true favorites. And with good reason! You need plant material that can withstand the slings and arrows Mother Nature sends its way — not to mention homeowner neglect or the abuse encountered on commercial properties. You need shrubs that are reliably hardy, disease- and pest-resistant and that flower profusely when they're supposed to.

Although that is a tall order, there are plenty of readily available flowering shrubs that meet these requirements. Because discovering them by trial and error can be an expensive and time-consuming process, I asked some green industry experts to share their experiences and suggestions. Here are their picks for beauty, reliability and toughness in shrubbery.

Hydrangea

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Tired of ‘Annabelle’? Don't have the right cultural conditions for ‘All Summer Beauty’ or ‘Nikko Blue’? Don't despair. There are some other great choices out there. For a change of pace, consider trying three cultivars of Hydrangea paniculata: ‘Pink Diamond’, ‘Tardiva’ and ‘Unique’.

Hydrangea paniculata are extremely durable plants,” notes Tim Boland, Curator of Horticulture at The Morton Arboretum in Lisle, Illinois. The arboretum began a hydrangea evaluation program in 1997.

This species has a combination of characteristics sure to endear them to landscape contractors: they're free of pests and diseases; they're hardy to -30°F; they adapt to a wide variety of soil conditions (although they prefer moist, well-drained soil), and they'll flower in partial shade. They also begin their spectacular flower show in late summer, when few other things are blooming, and they retain their flower heads until spring, providing interest through the winter. This species blooms on new wood, and the overall habit of the plant benefits from being cut back to the ground in late winter or early spring.

‘Pink Diamond’ has long white flowers that turn a deep, rich pink (sometimes almost purple) as they age. It matures at about 9 feet tall with an equal spread.

‘Tardiva’ is a prolific late-summer to early fall bloomer. Its white flowers have an airy, open look. This plant, similar in size to ‘Pink Diamond’, can be trained to a tree form.

‘Unique’ is the earliest bloomer of the three, typically beginning its show in late July to early August (see bottom photo, page 20). It has flowers similar to ‘Tardiva’, only bigger. Sometimes the flower clusters reach 12 inches in length. Over time, these flowers turn pink, although not as deep a color as ‘Pink Diamond’.

Physocarpus

Common ninebark (Physocarpus opulifolius) is a tough, profusely blooming shrub native to cold climes. ‘Diabolo’ (Physocarpus opulifolius ‘Monlo’) is of particular interest thanks to its distinctive purple foliage. Its resistance to disease and pests makes this shrub an excellent replacement for Prunus × cistena (purple leaf sand cherry).

“This shrub is extremely hardy, native, has colored foliage — which is hot right now — and it is gorgeous in flower,” reported Dave Grillaert, Nursery Facilities Manager at David J. Frank Landscape Contracting, Inc. in the Milwaukee area. “It has white flowers with a pinkish cast. Up against that foliage, it's dynamite.” Ninebarks adapt to a wide variety of soil types as long as they are in a well-drained location. This is a plant that, once established, actually prefers dry conditions. ‘Diabolo’ grows about 8 feet tall and 6 feet wide.

Roses

If you're looking for a shrubby plant with repeat blooming, good hardiness and excellent resistance to pests and diseases, it's hard to beat some of the shrub-type roses available today. (And don't forget those brilliant rose hips when considering fall color.)

‘Purple Pavement’ (Rosa ‘Rotesmeer’) is a favorite of Boland's. “It has performed very well for us at the arboretum,” he notes. This hybrid rugosa has large, semi-double mauve flowers with yellow stamens. A nicely rounded plant, it grows to about 3 feet in height and is hardy in Zones 3 through 7.

Grillaert is a fan of ‘Champlain’ (Rosa ‘Champlain’), a hybrid with dark-red double flowers. “This rose is so tough, I can dump snow on it all winter. It can die back to the ground, and by June, it will be 3 feet tall and flowering,” he notes. Grillaert prefers ‘Champlain’ to ‘Knock Out’ (Rosa ‘RADrazz’), the 2000 AARS (All-American Rose Selections) winner. “Last year, we had some trouble with ‘Knock Out’ roses that were on grafted stock. They weren't hardy,” he said. “This year, we have roses on their own roots. We'll see how they perform.” He notes that ‘Knock Out’ has a more uniform habit, which may make it popular with designers, and hybrid-tea-type foliage, which is often favored by homeowners.

‘Carefree Wonder’ and ‘Carefree Delight’ are two additional AARS shrub roses to consider. ‘Carefree Wonder’, a 1991 winner, offers hot-pink double flowers with a creamy-pink underside. This plant grows from 2½ to 4 feet tall. ‘Carefree Delight’, a 1996 winner, has vivid pink single flowers with a white eye. It has an arching habit and grows from 2 ½ to 5 feet tall. Both are hardy in Zones 4 through 7.

Spireas

Spireas are tough to beat because they are so pest-free and durable. But certain varieties are used quite extensively. If you're tired of ‘Snowmound’, ‘Little Princess’ and ‘Anthony Waterer’, try these two tough, but lesser known, species.

Fitch's spirea, also known as Korean spirea (Spiraea fritschiana), bears many large, white, flat clusters of flowers often tinged pink in late May to June (see photo, at right). “The flowerheads don't bloom uniformly, so that extends the bloom period,” Boland notes. The leaves are somewhat larger than ‘Snowmound’, and the plant has a more compact habit, growing 2 to 3 feet tall and up to 5 feet wide in a rounded form. The deep green leaves may have a bluish tinge. In fall, the leaves turn yellow, and sometimes even toss in a little orange, red or purple for good measure.

Grefsheim spirea (Spiraea × cinerea ‘Grefsheim’) is an early flowering shrub, offering white panicles (not the flat-topped flowers usually associated with spireas) in late April before the plant leafs out (see photo, at top). “This shrub is well-behaved; it flowers really early — around the same time as amelanchiers — and it's gorgeous,” said Grillaert. “It's like the best bridalwreath [spirea] in your grandma's garden but not so mangy.” This shrub grows to around 5 feet tall and 6 feet wide with graceful, arching stems. In fall, Grefsheim's leaves turn a brilliant combination of yellow, bronze and orange.

Lilacs

Preston lilacs (Syringa × prestoniae), also sometimes known as Canadian lilacs (because breeder Isabella Preston was from Canada) are an old, reliable and underutilized plant according to Richard Theidel, owner of Hinsdale Nursery in suburban Chicago. “The Canadian lilacs make beautiful hedges; they flower a little later than the common lilacs, and they don't get powdery mildew. They're good plants,” he notes. They also are hardy to Zone 2. Canadian lilac flowers tend to hang or nod. The foliage is long, narrow and slightly ruffled. Theidel's favorite cultivar is ‘James MacFarlane’, a clear-pink flowering form with a mildly spicy fragrance. This plant grows to 8 feet tall and about 6 feet wide.

‘Tinkerbelle’ (Syringa ‘Bailbelle’) is a new and slightly smaller dwarf lilac introduced by Bailey Nurseries. Its wine-colored buds open to spicy, pink flowers in mid- to late spring (see top left photo, page 18). The upright plant has green, heart-shaped foliage with good disease resistance. It grows about 5 feet tall with an equal spread. Well-drained soil is critical to good performance.

Viburnum

There are so many kinds of viburnums, a person could spend ages sorting them all out. You may already be using Koreanspice viburnum (Viburnum carlesii), Judd viburnum (Viburnum × judii) or highbush cranberry (Viburnum trilobum). Here are three more that get high marks from people in the green industry.

‘Autumn Jazz’ Arrowwood viburnum (Viburnum dentatum ‘Ralph Senior’) offers not only spring flowers but also spectacular fall color (see photo, above) and abundant fruit. This shrub produces creamy white, flat-topped flowers in May to early June. Its whorled leaf arrangement gives it a slightly different character than other V. dentatum varieties. The flowers are followed by shiny, blue-black fruit. In fall, ‘Autumn Jazz’ turns yellow-orange to red to burgundy for quite a show. ‘Autumn Jazz’ is an introduction of Chicagoland Grows, a plant selection program sponsored jointly by the Morton Arboretum, the Chicago Botanic Garden and the Ornamental Growers Association of Northern Illinois. This shrub, which grows 8 to 10 feet tall with a 10- to 12-foot spread, is among the more shade-tolerant of the viburnums. The Morton Arboretum's Boland cautions purchasers to look for cloned plants — not those grown from seed. “The arrowwoods tend to exhibit a lot of variability when grown from seed,” he explains.

Viburnum sargentii ‘Onondaga’ is a shrub that intrigues Ric Gesch, yard supervisor at David J. Frank Landscape Contracting Inc. near Milwaukee. In May to June, this U.S. National Arboretum introduction develops reddish-purple flower buds that open to pink-tinged, white lace-cap flowers. Next come large clusters of bright red fruit that persist through winter. In fall, this shrub turns yellow to red. One of the things Gesch likes about this upright, rounded shrub is its maroon-colored spring foliage which matures to green with a purplish cast. ‘Onondaga’ matures to 12 feet tall with a 6-foot spread. Hardy in Zones 3 through 7, this shrub is free of pests and diseases and performs best in moist soil.

Viburnum plicatum var. tomentosum ‘Summer Snowflake’ is a shrub Jennifer Brennan, horticulture information specialist at Chalet Nursery in suburban Chicago, frequently recommends to her retail customers. “It starts flowering in June and keeps going through the summer,” said Brennan, who also likes the plant's horizontal branching structure (see bottom photo, page 22). This plant, which grows about 8 feet tall, has red to black berries and burgundy fall color. Boland notes that it has a narrow habit and is a great choice next to doorways. He adds that it sometimes dies back to the ground in Zone 5 (resprouting in spring), so he recommends growing it in protected areas.

If you're looking for a smaller viburnum, Grillaert recommends Newport Dwarf Doublefile Viburnum (Viburnum plicatum ‘Newzam’). This rounded, compact dwarf grows 4 to 5 feet tall. In spring, it has showy, snowball-like flower clusters. Its leathery green foliage turns burgundy in fall. It is hardy in Zones 5 through 8.

Next time you are feeling a little bored by your tried and true favorites, why not see whether some of these selections can add some variety and interest to the landscape? You might even find a new favorite…or two.

Patrice Peltier is a client services representative with David J. Frank Landscape Contracting Inc. (Germantown, Wis.).

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