Plants Worth Your Time

Without a doubt, plants are the foundation of the landscape industry, and the diversity of ornamental species and cultivars on the market allows for creative and appealing landscape compositions. Thumbing through trade magazines can be a productive way of learning about new plants or gaining new insights regarding common ones. Every member of our industry has his or her favorites, and it is interesting to hear their justification for selecting and promoting specific plants.

WHY THAT PLANT?

People have their own reasons for selecting particular plants. Consumers may be attracted to a plant's ornamental appeal, while designers may be more focused on the purpose or function a plant will serve in the landscape. Landscape managers may select plants for their overall performance and ease of care.

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When asked to recommend plants, I usually respond with several questions. I tend to follow a sequence that proceeds from function to maintenance requirements. It is not as simple as blurting out a few names; I usually identify my selections on the basis of ornamental quality, adaptability and management.

Function, or use, and the amount of available space help guide me to choose a plant type such as tree, shrub or groundcover. After function, I consider the aesthetic qualities of the plant such as form, foliage, flowers, fruit and bark. Consideration of plant aesthetics logically leads to a site evaluation and determining whether the plant will be able to perform given the particular conditions of the site.

Throughout my educational career, my plant professors could be overheard emphasizing “Don't fight the site.” If you go against Mother Nature and fail to match the plant with the site conditions, there is no doubt that you will lose. Site adaptability factors such as hardiness, soil tolerance, exposure and light levels define whether aesthetic selections will actually perform to expectations.

The final consideration in plant selection is management. When we consider landscape development, it is the landscape manager who directs the development of the landscape. After initial establishment, accent plants start to show off their qualities: masses integrate, and border plantings achieve their intended shape. It is the feasibility and quality of maintenance that ensures the long-term aesthetic appeal of any plant.

The following are a few plants to consider in the landscape. I've chosen to include them here for their various exceptional qualities. Keep in mind that it's up to you to determine whether they will adapt to a specific site you have in mind. However, they have performed well under our conditions here in Michigan and we definitely consider them worth some thought.

FLOWERING SHRUBS

The genus Rhododendron provides a wide array of plants for the landscape. They may be evergreen or deciduous, and exhibit a variety of habits, leaf sizes and flower colors. Generally, we think of rhododendrons and azaleas as temperamental. Low temperatures, exposures and soil pH often limit their use to specific sites or protected microclimates.

However, we have had the opportunity to work with a group of deciduous azalea hybrids developed in Minnesota and are extremely pleased with their ornamental display and growth performance. They are referred to as the Northern Lights hybrids and are the result of crosses between Mollis hybrids (Rhododendron × kosteranum) and the Roseshell azaleas (Rhododendron prinophyllum roseum) made by the late Albert G. Johnson in 1957. The Mollis hybrids are deciduous and similar to the Exbury group. The colors of the common cultivars are white, yellow, pink and red. The Roseshell azalea is a spreading shrub, ranging in height from 2 feet to 8 feet. The flowers are bright pink and fragrant. It is native from New Hampshire and southern Quebec to Virginia and west to Illinois. Hardiness is reported from Zones 3 to 8.

Northern Lights has benefited from the flower characteristics and hardiness of its parents. Northern Lights possesses a compact growth habit, about 6 feet in height and spread. The flowers are 1Ω inches across, borne in clusters, and appear in late May and early June. Harold Pellett, executive director of the Landscape Plant Development Center in Chanhassen, Minn., proclaims that, “Northern Lights hybrids are the only winter hardy azaleas that can be counted on to produce full bloom every year in the Upper Midwest.” Flower buds are reported hardy to -45°F. Pellett also indicates that even though azaleas require acid soil for optimum growth, these plants will grow well in neutral pH soils amended with acid peat and given an annual acidic fertilization.

‘Pink Lights’, ‘Rosy Lights’ and ‘White Lights’ were the first clones named in the Northern Lights series, which entered the trade in 1984. ‘Pink Lights’ and ‘Rosy Lights’ are similar in habit and hardiness to the original group. ‘White Lights’ is a selection from a cross between Rhododendron prinophyllum and a white-flowered Exbury azalea. Flower buds are light pink, fading to white in full bloom. ‘Orchid Lights’ is a compact azalea from the cross between Rhododendron canadense and Rhododendron × kosteranum. Plants average 3 feet in height with equal spread. Orchid colored flowers bloom in mid-May. ‘Golden Lights’ and ‘Spicy Lights’ are pleasant additions to the series, with their golden yellow and salmon colored flowers. ‘Golden Lights’ matures at about 4 feet, blooms in late May and has a reported hardiness of -30°F. ‘Spicy Lights’ is a larger shrub, closer to the original Northern Lights with a height of 6 feet. ‘Spicy Lights’ blooms in late May or early June with bud hardiness to -35°F.

Callicarpa dichotoma, purple beautyberry, is a plant that has generated some interest in our Midwestern gardens. Beautyberry is a graceful medium-sized shrub that grows to about 3 feet. It has a rounded crown with slender, purple, arching branches and gets its name from the small, pinkish-lavender flowers that give rise to lilac-violet, porcelain fruit. Beautyberry is an adaptable shrub with reported hardiness from Zones 5 to 8.

In Mid-Michigan we treat it as a dieback shrub and prune it to the base every spring. Even though annual renovation may be a chore, it results in the same graceful arching form each year. Its impact on the landscape is worth the few minutes of pruning.

The two cultivars that have generated specific interest in our market are ‘Issai’ and ‘Early Amethyst.’ ‘Issai’ is a heavily fruited compact introduction, and ‘Early Amethyst’ fruits earlier with bright purple berries.

Witchhazels have been a favorite of mine for a long time. They offer an interesting flower display, tolerate a wide range of soils from dry sands to poorly drained clays and perform well in full sun or as an understory plant in partial shade. Depending on your perspective, they can be considered large shrubs or small trees. We have had positive experiences with a number of the species and cultivars. Hamamelis virginiana, common witchhazel, is a North American native offering a fall season of yellow flowers and foliage. Hamamelis vernalis, another native, is noted for its late winter yellow-orange flowers.

The Intermedia hybrids resulting from crosses between H. japonica and H. mollis are truly worth considering. They possess the same site tolerances as their North American relatives and late-winter flowers ranging in colors from yellow to red. Their ornamental appeal returns in the fall with equally spectacular fall foliage displays from yellow to mottled reds. ‘Arnold Promise’ is probably the most noted cultivar with its clear yellow flowers. ‘Diane’ is one of the best red flowering forms, and ‘Jelena’ has long, coppery, strap-like petals. Hamamelis mollis ‘Pallida’ has also pleased us with its soft sulfur-yellow petals emerging out of a reddish-purple calyx cup.

EVERGREEN SHRUBS

It is easy to understand the popularity that evergreen shrubs have had in the landscape. Year-round foliage, flower and leaf color, and a multitude of forms make evergreen shrubs a staple in most landscapes. The following plants are consistent performers that play supporting roles in landscape compositions.

Ilex glabra, inkberry holly is heralded as a broad-leaved evergreen that likes wet soils. Its tolerance of adverse soil conditions makes it extremely useful in both suburban and urban areas. Inkberry is an upright shrub with a rounded top. Its size varies, but it may attain 6 feet with an 8-foot spread. Leaves are evergreen, shiny and dark green. As with most broad-leaved evergreens, protection from winter desiccation is important. Because the species tends to become leggy and lose its lower foliage, cultivars are preferred for their compact and dense growth. ‘Compacta’ is probably the oldest and most popular cultivar.

Princeton Nurseries introduced it in the late 1940s. ‘Compacta’ forms a tight mound of about 4 feet. However, it may also become leggy with age and lose its lower foliage. Light pruning can enhance foliage retention and form. Nordic (‘Chamzin’) is a selection from Lake County Nursery in Perry, Ohio, that has a compact form and lustrous, deep-green leaves. It has a broad, pyramidal growth habit and maintains its dark-green color throughout the winter. ‘Shamrock’ is another compact form with bright green new foliage and glossy, dark-green older foliage. This plant is a little slower growing than ‘Compacta’, reaching approximately 3 to 5 feet in height.

Taxus (yews) are hardy, evergreen shrubs with excellent foliage characteristics and a variety of species and cultivars. However, when I think of Taxus, I think of pruning and that several of the cultivars generally require a little more pruning than I am willing to provide. To that end, we have searched for a few Taxus species or cultivars that require minimal pruning and still offer dense foliage characteristics. Taxus baccata, the English yew, is most noted for its tree form specimens in England. It is found on old estates and in botanical gardens and arboretums, but is not used to any great extent in landscapes. T. baccata ‘Repandens’ is dwarf, slow-growing cultivar with glossy, dark-green foliage that appears to lay flat on its stems. ‘Repandens’ is considered the hardiest form of T. baccata. Its branching habit is more horizontal with a descending pattern that creates an interesting mound shape. Several specimens in our gardens are more than 20 years old and still maintain an attractive appearance despite never having been pruned.

Taxus cuspidata, the Japanese yew, has a number of cultivars, with the most noted being ‘Capitata’, the pyramidal form. The cultivar of particular interest in our search is ‘Monloo’, an extremely low-spreading form, marketed under the trade name Emerald Spreader. It has dark-green needles, is slow-growing and reported to be hardy to Zone 4. Michael Dirr gives an example of a 20-year plant that is only 30 inches in height. It has been used in different planting situations where it continues to look quite attractive with minimal care.

Taxus × media and its cultivars most likely provide the widest selection of Taxus on the market. ‘Densiformis’ is certainly a staple of the Midwestern landscape. The cultivar that we found particularly useful is Taxus × media ‘Tauntonii’. The ‘Tauntonii’ yew is a low-growing, spreading form that provides year round foliage and seasonal backdrops for perennials and annual plantings. ‘Tauntonii’ is more controlled in its growth, without the aggressive, upright and spreading growth seen in other ‘Densiformis’-like cultivars.

This is a small selection of plants for consideration. Each its place in the landscape; some serve as accents, others in a supporting role. In any case, they have served us well from both an aesthetic and a management perspective.

Dr. Robert E. Schutzki is professor of ornamental horticulture at Michigan State University (E. Lansing, Mich.).

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