Heuchera, commonly called coral bells or alumroot, is a genus consisting of about 55 species (exact numbers vary) of evergreen to semi-evergreen herbaceous perennials, all native to North America. In fact, coral bells were one of the first plants exported back to Europe in the 1600s by early American explorers. Different species exhibit attributes that are specialized to their native areas. For example, some species are not bothered by heat and humidity; others perform well at high elevations; others can tolerate more sun. Yet, cultivars sometimes combine species from different regions, which can make hardiness a concern.
Heuchera is dominated in the trade by a profusion of cultivars. Hundreds of cultivars have been introduced since the 1990s, the majority with an emphasis on ornamental foliage. In fact, the straight species are difficult to find outside of nurseries that specialize in native plants.
Most Heuchera cultivars are based primarily on 4 main species for parentage, two of which are native to Virginia. This article will:
- Discuss the characteristics and care issues common to different species of Heuchera
- Describe species native to Virginia
- Introduce two other species primarily used in cultivar development
- Demonstrate how the characteristics of different species are exhibited in cultivars
- Highlight several field trials that evaluated cultivar hardiness and vigor
GENERAL CHARACTERISTICS
A member of the saxifrage family (Saxifragaceae), some of Heuchera‘s cousins include the genera Ribes (gooseberry and current), Astilbe (false spirea), and Tiarella (foamflower). (For more information on the native plant Tiarella, see this article from The Garden Shed.) While some species are known for floral display, most are known for their ornamental foliage. In addition to a beautiful range of colors, leaf shape, size, and textures, many Heuchera display a color change through the season from the bright colors of spring to the mature, darker leaves of midsummer. Individual tiny flowers are bell-shaped and appear in spring to summer in panicle inflorescences, which means a cluster or grouping of flowers along the stem. Flower color and the amount of flowering differ by species. A high tannin content gives the foliage a bitter taste that makes it unappetizing to deer. Rabbits sometimes feed on floral stems. Plants tolerate juglone and can grow well in the dripline of the black walnut (Juglans nigra). The roots of some species contain the mineral substance alum, a powerful astringent that was used medicinally to treat wounds, sores, nose bleeds, and gastrointestinal ailments.
GENERAL CARE
Most species are happiest growing in moist, well-drained organic soils in partial shade or morning sun. Heuchera grows in USDA Hardiness Zones 4-9 and is usually “evergreen” in Zones 7-9. “Evergreen” is a term that may promise more than what is delivered; Heuchera often lays flat in winter winds and sometimes heaves out of the ground from wind and desiccation. Some species will grow in full sun, especially in the northern half of the country, if the soil is kept consistently moist. In zones 7-9, Heuchera does best when protected from hot afternoon sun; leaf scorch can be a problem. In general, plants with darker colored foliage can withstand more sunlight. Good drainage is essential to good health; crown rot may be a problem if soils do not drain adequately.
ROOT CARE AND DIVISION
Coral bells are shallow-rooted, and their woody crowns are held above the soil as the plants age. A thick woody stem with noticeable rings grows up from the crown and gets longer each year. As it grows, it can become more fragile and more vulnerable to desiccation. Coral bells tend to be short-lived and may need to be rejuvenated every 3 to 4 years. You can dig up the plants and replant them a little deeper, with 1-2” of the stem sticking out of the soil. You can also lift the entire clump, cut away the older root stalks, and replant the youngest growth.
HISTORY OF HEUCHERA CULTIVAR DEVELOPMENT
In the 1980s, North Carolina nursery owner Nancy Goodwin found a naturally hybridized Heuchera seedling that had dark leaves with silver markings. It was found in her garden between two cultivars, H. americana ‘Dale’s Strain’ and H. micrantha ‘Palace Purple’. This naturally hybridized cultivar, ‘Montrose Ruby’, showed plant growers that they could develop exciting new foliage colors by crossbreeding two or more different Heuchera species.
BACKGROUND ON CULTIVAR DEFINITIONS
I contacted Ian Caton, a native plant nurseryman in Floyd, VA, with questions about Heuchera cultivars. To meet the definition of cultivar, which means cultivated variety, a plant must be bred asexually. Ian explained that H. micrantha var. diversifolia ‘Palace Purple’ is propagated asexually, which involves taking a part of one parent plant and causing it to regenerate itself into a new plant. H. americana ‘Dale’s Strain’, H. villosa ‘Autumn Bride’, and H. villosa ‘Bronze Wave’ are examples of Heuchera that have origins as purely wild plants with characteristics that pass along fairly well, generation after generation from seed. ‘Dale’s Strain’ is almost always propagated by seed. Although ‘Autumn Bride’ comes true from seed, and is sometimes still propagated that way, it is also propagated asexually which is more volume efficient. ‘Bronze Wave’ shows phenotypic variation, which, on a practical level, means its seedlings can show a variety of foliage colors. Therefore, this plant is propagated asexually to achieve more uniformity for sale in nurseries. These examples show the complexity of the cultivar label! In general, species or seed-grown strains of a particular species are going to be very hardy.
PLANT VIRGINIA NATIVES CAMPAIGN
This campaign is an effort to help Virginia gardeners identify plants native to their area. Watch for an article about the Campaign in next month’s Garden Shed. For inclusion on the list of recommended plants, cultivars of straight species have been vetted to ensure they are ecologically viable, meaning their leaves and flowers contribute to the food web and do not negatively alter insect behavior. Two heuchera cultivars are included on this list: ‘Dale’s Strain’ and ‘Autumn Bride’. As described in the section above, ‘Dale’s Strain’ and ‘Autumn Bride’ are seed strains, although they may be labeled at nurseries as cultivars.
SPECIES USED IN CULTIVAR DEVELOPMENT
Although there are now hundreds of Heuchera cultivars, four native species (out of over 50 species) are the primary contributors to cultivar development: H. americana, micrantha, sanguinea and villosa. Let’s now look at these four species in more detail, with particular emphasis on the two main species native to the southeastern U.S., and two other native species found in this area.
HEUCHERA SPECIES NATIVE TO SOUTHEASTERN U.S., INCLUDING VIRGINIA
H. americana
Commonly called alumroot, coral bells, and rock geranium, this species is native to the southeastern U.S., including Virginia, but is hardy in many parts of the country. According to the Digital Atlas of the Virginia Flora, it is frequently to commonly found in the mountains and in the Piedmont; it is infrequent in the inner Coastal Plain and rare to absent in the outer Coastal Plain. According to the Native Plant Finder by Zip Code, it is native to Albemarle County. In nature, it can be found growing in shade to partial shade in rocky forests and rock outcrops, particularly where soils are acidic. It has a clumping habit and grows 1-3’ tall and 1-1.5’ wide. Heart-shaped leaves emerge flushed with purplish-brown and mature to a uniform green. Tiny flowers are greenish or creamy with a pinkish tint. This species has been used as a component of modern hybrids to lend hardiness, vigor, and color.
H. villosa
Commonly called hairy root alum or maple-leaved alum, this species is native to rocky wooded slopes in the Eastern United States from New York to northern Georgia. According to the Digital Atlas of Virginia Flora, H. villosa is common in the mountains of southwest Virginia, becoming less common northward to Rockingham County and infrequent to rare in the inner southern Piedmont. According to the Native Plant Finder by Zip Code, it is native to Albemarle county. It grows best in part shade or filtered sun in moist, well-drained, humus-rich soil. H. villosa is heat and humidity tolerant, a desirable characteristic for cultivar selection. It is one of the largest alumroots, growing 1.5-2.5’ tall and 1-2’ wide. It has hairy leaves that are often compared to maple leaves. Its form is more open than mounding. Breeding has led to various different shapes and sizes of Heuchera. Tiny, whitish to pinkish flowers appear in mid- to late summer, which makes this one of the latest-blooming Heuchera.
OTHER SPECIES NATIVE TO SOUTHEASTERN U.S.
H. longiflora
Commonly called long-flowered alumroot, this species is native from southern Ohio to Alabama, but is rarely found in the wild. In Virginia, it is limited to the mountains of the far southwest, where it is frequent. It is very similar in size and color to the more well-known H. americana. The main difference is that the individual flowers of H. longiflora are larger and held on stems that are shorter than H. americana. It blooms May-June. Foliage is green with dark green veining, sometimes with a silverish overlay.
H. pubescens
Commonly called downy alumroot, this species is native to Virginia at elevations of 3,000-4,000′. It is frequent in the mountains, rare in the inner Piedmont. It grows 8-14” tall and has short flower clusters of showy white individual florets; blooms July-August. The foliage has an attractive purple-red color in winter.
OTHER SPECIES USED IN CULTIVAR DEVELOPMENT
H. micrantha
Commonly called crevice alumroot, this species is native to western North America from British Columbia to California, where it grows on rocky slopes and cliffs. Its foliage varies from green to reddish green or purplish green. Although this species is frequently used for color in the development of hybrid cultivars, it tends not to perform well in warmer climates. H. micanthra ‘Palace Purple’ ignited great interest when it won 1991 PPA Perennial of the Year, and inspired a wave of Heuchera cultivar development.
H. sanguinea
Commonly called coral bells in reference to this old-fashioned species’ showy, sweetly fragrant, deep pink to red bell-shaped flowers which appear in late spring and can last through early summer (May-July). The flowers are a nectar source for bees and hummingbirds. H. sanguinea is known for its floral displays more than for its foliage, although it has interesting green, heart-shaped or roundish leaves. It grows 9”-2.5′ tall and 1-1.5′ wide. Native to the southwestern U.S., it grows in full sun to partial shade in well-drained soil with high organic content. Field trials by the Chicago Botanic Garden found a tendency for stem rot among cultivars with this species in their parentage.
FIELD TRIALS
Chicago Botanic Garden
Richard G. Hawke of the Chicago Botanic Gardens headed a comprehensive evaluation of 64 Heuchera species and cultivars from the spring of 1995 through the autumn of 2000. The study evaluated hardiness and vigor factors, as well as ornamental traits. The results of this study and cultivar recommendations can be found at this link.
University of Vermont
In 2008, Dr. Leonard Perry at the University of Vermont started a field study of 112 Heuchera cultivars, including a few Heucherella cultivars, in response to growers’ concerns about cold hardiness. See this link for more details.
Mt. Cuba Center
Headed by George Coombs, now Head of Horticulture at the Mt. Cuba Center, these trials evaluated 83 different Heuchera cultivars over a 3-year period from 2012-2014. The focus was on identifying the best cultivars for mid-Atlantic gardens, and to that end, cultivars were selected whose parentage came from the two primary species native to the southeastern U.S., H. americana and H. villosa.
Top field trial performers were: ‘Citronelle’, ‘Cajun Fire’, H. villosa ‘Bronze Wave’, ‘Color Dream’, and Steel City’. See this link for more details on this study and its results.
HOW TO USE
Large alumroots have a dramatic effect when planted en masse in the garden and are effective companions for plants with very showy blooms. The mounding species like americana can be used as accent plants, while the species with more open habits — like villosa — can be easily interwoven with other plants. Heuchera also performs very well in containers where moisture and exposure to sunlight can be controlled.
POLLINATOR BENEFITS
While the flowers of most species of Heuchera are secondary to the foliage, the nectar and pollen of the flowers attract small bees, including Halictid bees and the native Heuchera specialist bee Colletes aestivalis (only interested in native Heuchera). Species with red flowers are a nectar source for hummingbirds. Heuchera species are also visited by flies and wasps. H. Americana and H. villosa are hosts for 1 moth caterpillar in Albemarle county, Epinota heucherana Heinrich, 1923.
PESTS AND DISEASES
Root rot can be the most challenging problem. Black vine weevil is a notorious garden pest for a lot of genera, including Heuchera. Vine weevils make a characteristic D-shaped hole in the leaf which indicates that there are adults feeding on the leaves. Larvae are more destructive, feeding on roots deep in the soil in the winter. See this link for more information.
SUMMARY
All species of Heuchera are native to North America with different species exhibiting attributes that are specialized to their native areas. Although it is difficult to find straight species in the trade, native nurseries are a good source. See this list of Native Plant Nurseries compiled by the Virginia Native Plant Society. H. americana and H. vilossa are the two main species local to the southeastern U.S., including Virginia. Hundreds of cultivars are available, mainly with enhanced foliage color and form. Flower colors and the amount of flowering vary by species, with H. sanquinea, a southwestern native, best known for its floral displays. The combination of parent species will affect the hardiness and adaptability of cultivars to different regions. Most species are happiest growing in moist, well-drained organic soils in partial shade or morning sun. Although a perennial, Heuchera and its cultivars can be effectively used in container plantings, allowing control over moisture and sun exposure.
SOURCES
Digital Atlas of the Virginia Flora
Native Plant Finder According to Zip Code
Ian Caton, Wood Thrush Native Nursery
“Landscape Plants Rated by Deer Resistance,” Rutgers University.
“Heuchera,” Field Trials, Mt. Cuba Center
“The Results Are In: Heuchera is a Great Alternative for Shade Gardens,” Mt. Cuba Center
“Evaluating Native Plants at Mt. Cuba Center with George Coombs,“ a 2014 Interview by Margaret Roach, A Way to Garden.com
“The Best Heuchera and How to Grow Them, with Mt. Cuba Center,” a 2015 interview with George Coombs by Margaret Roach.
“An Evaluation Study of Coral Bells,” Plant Evaluation Notes (2003), Richard G. Hawke, Chicago Botanic Garden
“Vermont Heuchera (Coralbells) Trials 2013,” Dr. Leonard Perry, University of Vermont
Heuchera americana, NC State Extension
Heuchera villosa, NC State Extension
Heuchera sanquinea, NC State Extension
Lady Bird Johnson Wildlfower Center Native Plant Database
Heuchera micrantha, CALSCAPE, California Native Plant Society of Sonoma County
Heuchera pubescens, Lady Bird Johnson Wildlife Center Native Plant Database
Heuchera americana hirsuticaulis, Woodland Alumroot, Illinois Wildflowers
Heuchera longiflora, Long-flowered Alumroot,” Mt. Cuba Center
“Black Vine Weevil,” Virginia Cooperative Extension
Colletes aestivalus, USGS Native Bee Lab
FEATURE PHOTO: Heuchera americana, Bernice Thieblot, Quarry Gardens at Schuyler, VA
