Often overlooked for use in the cultivated landscape, native sumac is a tough and beautiful shrub with multiseason interest in nearly any setting. Trials at Longwood Gardens helped to determine the best species for the trade.
The fruits of Rhus glabra can be used to make a drink sometimes called sumac “lemonade.”
It can take a while for plants native to an area to catch on as landscape plants in the regions where they are found growing naturally. This may be because we are always looking for something new or different, while ignoring common plants growing around us. Some of these native plants get improved upon through selection and breeding and released into the trade; others slowly grow on us for their beauty and rugged durability. Species of sumac (Rhus) native to the eastern United States seem to have accomplished both of this recently, and after many years of being appreciated in Europe, it is refreshing to see them in various landscape settings in America.
A true comparison
Until recently, there were not many new cultivars of sumac from which to choose. Most cultivars on the market consisted of cut-leaf forms of the species. To help select the best Rhus for use in the landscape, Longwood Gardens in Kennett Square, Pa., (Zone 6) conducted shrub trials from 1999 through 2006. Seventeen taxa of Rhus were grown and evaluated by staff, students, horticulture professionals and volunteers. Fourteen taxa were started in the trial, 10 of which are native to the eastern United States. Three of each species or cultivar was planted for the trials. Plants were placed in an open field in full sun, and once established were minimally maintained.
Evaluators in the trials were asked to consider many aspects of the plants throughout the seven-year period. Data were collected on size, growth habit, stems, foliage, flowers and fruits based on the appearance of the plants. All of these aspects were rated on a scale of 1.0 to 5.0, and an overall rating was also given for each date of evaluation. Participants were instructed to rate the plants as: 1.0 = “unattractive,” 2.0 = “acceptable,” 3.0 = “attractive,” 4.0 = “very attractive” and 5.0 = “best in class.” Notes were also made about any injury, pest or pathogen problems and culture, and specific comments were made on any aspect of the plant being evaluated.
Fragrance and resilience
One of the shrubs to be evaluated was Rhus aromatica (fragrant sumac.) It is a shrub that grows 2 to 6 feet in height and 6 to 10 feet wide, in moist or dry, average soils. In its natural setting, this shrub is seen at the forest edge, in dry uplands and on rock outcroppings in much of the eastern United States. Fragrant sumac is a spreading shrub that readily suckers from the roots, and these masses can become quite dense. This helps the species to be very good at stabilizing soil, once established.
The flowers of fragrant sumac are a pale yellow. Male flowers are borne from short catkins at the end of stems and in terminal leaf axils that form in late summer. Female flowers are short panicles at the ends of branches. Plants flower in early spring before or while leaves are just appearing. Emerging, trifoliate leaves have a reddish color, and the terminal leaflet is slightly longer than the leaflets on either side. Through summer the leaves are a rich green, glossy on the upper surface and fuzzy underneath. They are 3 to 5 inches long, coarsely toothed and are aromatic when crushed or bruised. In fall the leaves turn shades of burgundy, red and orange. In large plantings, all colors in this range can often be seen at once.
Small panicles of fruits develop in late summer. The drupes are red and covered in hairs. They persist through the winter, but may lose the vigorous red color. Fragrant sumac can be mistaken as Toxicodendron radicans (poison ivy) to the untrained eye, because it also has trifoliate leaves. However, poison ivy’s leaves are produced on a long stalk and it has clusters of white drupes in late summer, whereas fragrant sumac bears panicles of reddish drupes.
Fragrant sumac has no serious insect or disease issues. These shrubs seem little affected by things like poor, sandy soils and road salt. This species is usually planted in masses and definitely looks better in groups rather than as a specimen plant. If spaced well with room to grow, plants will spread and fill in quite nicely. Plants covering a large slope can even handle being mown every few years, and come back rejuvenated.
The beautifully cut leaves of Rhus glabra ‘Laciniata’ are a bright green with contrasting red-pink new stems and leaf rachis.
PHOTOS COURTESY OF LONGWOOD GARDENS.
During the trials at Longwood Gardens, the species R. aromatica scored second highest overall, with an average of 2.7 out of 5.0. It received its highest score in the spring of one year with some positive comments about its upright, open form. At that time flower buds were present, but flowers or leaves had not emerged. In the late spring of another year a low score was given concerning form, as the evaluator described the form as “messy.” In general, evaluators differed in their perception of the growth habit, and their comments ranged from positive to negative. Most of the higher ranking occurred during flowering time in spring or throughout the summer, with most positive comments about the flowers, which were described as “elegant” and “delicate-looking.” Surprisingly, there was not much mention about the fall color of the leaves, and the species received an “attractive” score only one year; this evaluation also mentioned the red fall color of the leaves into November.
There are a few cultivars of fragrant sumac available, two of which were started in the shrub trials conducted at Longwood Gardens. ‘Konza’ is a cultivar selected by the USDA Plant Material Center in Manhattan, Kan., in 1980 for greater fruit production and vigor. It was presented for use in the Midwest as screens and for erosion control. This cultivar reaches 10 feet tall and can spread even wider. Although included in Longwood’s trials, ‘Konza’ failed to thrive after just three years.
One cultivar commonly seen along landscaped slopes or parking lot plantings is ‘Gro-Low’. Introduced by Synnesvedt Nursery Company in Round Lake, Ill., it is indeed low growing. It reaches no more than 2 feet tall and spreads to 8 feet. During the Longwood trials, R. aromatica ‘Gro-Low’ ended up with an average rating of 2.5, but received a high rating of 4.0 twice. Most of the positive evaluations addressed attractive foliage and stems. Some of the lower scores were received during the early spring, as plants were seen as untidy. This can be corrected in the home garden by removing some suckers arising from the roots with a sharp spade about once a year, or even just by mowing around the edge of a planting.
Up in flames
Rhus copallinum (shining sumac) is a large shrub or small tree that can reach to 20 feet tall and wide. If seen along the side of a road in fall, it will definitely turn heads with its unbeatable, bright red foliage. The leaves are pinnately compound, 6 to 12 inches long and have a distinct, winged rachis. The individual leaflets are smooth edged, and the whole leaf has a high gloss finish. In summer the shining leaves are a deep green, but once autumn arrives the leaves turn a burning red, hence the plant’s other common name: flameleaf sumac. The stems of shining sumac are covered with fine hairs, as are the undersides of the leaves. Flower panicles are pyramidal and up to 8 inches long. Greenish white flowers appear from July through September and stand out against the dark background of the foliage. After flowering, panicles of small, red drupes are produced on female plants; these then are eaten during the winter by birds and mammals, especially during harsh, snow-filled months.
Shining sumac does colonize as all species of sumac tend to do, but in a landscaped or garden setting, pruning out undesired suckers is a simple task. At planting time, careful consideration has to be made for spacing, so remember the spread can be 10 to 20 feet if plants are left to colonize. This species wants to be in full sun but also grows in part shade. A nice shrub with great fall color can be achieved with minimal effort. The one thing sumac might not like is an overdose of nutrients or water.
Two different groups of shining sumac were grown in the trials at Longwood Gardens; one was collected from the wild, and one was bought in from a nursery. There were no cultivars of R. copallinum in the trials, although some can be found today. The average rating for both groups together was 2.4 out of 5.0. In summer and again in the fall, the leaves’ gloss and color were noticed and rated positively. In October of one year, a group of shining sumac received a rating of “best in class,” based on the leaves – and about the attractiveness of the fruits. Although fruits were regarded as attractive in the fall, they were not seen that way during the spring, as the clusters tend to droop after fall turns into winter and the red color fades. Some evaluators liked the open, vase-shaped habit, calling plants “graceful” and “interesting,” while others could not see past the many suckers that had developed. It should be noted that both groups of shining sumac suffered a bit of dieback one year, which may have lowered the overall average of scores.
A range of fall colors can be seen on the leaves of Rhus aromatica ‘Gro-low’ alongside the catkins of next spring’s fl owers.
Rhus glabra (smooth sumac) grows to be a small tree or large shrub, to 15 feet tall and wide. It has an upright, open form and thick stems. The large, compound leaves of smooth sumac are a clear green, 12 to 18 inches long with toothed edges, and are glaucous on the undersides. Once summer starts to turn to autumn, the bright reds and oranges of smooth sumac foliage shine along most roadsides. Unlike the previous species discussed, the rachises of the leaves are not winged, and the stems are smooth. Young stems are green with a bloomy, blue appearance, and the rachises are reddish. Older stems are gray and covered with numerous lenticels. Flowers are borne in pyramidal, upright yellow-green panicles in summer and can be up to 1 foot long. The developing fruits will persist into the winter, providing an emergency food source for overwintering birds and other wildlife.
Four groupings of smooth sumac were included in the Longwood trials. Two groups included the straight species, and the other two groups consisted of R. glabra ‘Laciniata’. This is a very old cultivar that was discovered in 1863 near Philadelphia. It is a form with leaflets deeply cut, appearing almost doubly pinnate. One group of ‘Laciniata’ was ranked third out of all sumacs, with an average rating slightly over 2.6, and a group of the species came in close behind at number four with an average rating of 2.6.
Most of the higher rankings and positive comments were made during the summer and fall months, and most comments were about the leaves; of these comments, many mentioned the attractive summer color and the pink or reddish rachis. Leaves were particularly appreciated for their cut-leaf form and were said to be “lacy,” “beautiful” and “awesome.” The red fall color was highly noted for all groups of plants, and the bronze color of the new growth was also appreciated. Many participants noticed that bees and butterflies frequented the flowers, and plants were noted for their architecture during winter. Most negative comments addressed suckering or weedy habits.
The compound leaves of Rhus typhina have toothed leafl ets and a pinkish pubescent rachis.
Staghorn sumac (R. typhina) is similar to smooth sumac in habit and habitat. This species however, can grow up to 30 feet tall and may attain an equal spread. It is found growing in the same locations as smooth sumac, but is not as common. This sumac will tolerate almost any type of soil unless it is poorly drained. Staghorn sumac is known to colonize an area when left on its own, and spreads by sprouting from its extensive lateral root system. This plant needs to have space for it, and its root system, when it is planted and does very well when left to colonize an open area or slope. The compound leaves of staghorn sumac are larger than smooth sumac at 18 to 24 inches long, giving an almost tropical feel to plantings. The leaves are bright green and paler underneath, with leaflets being toothed on the edges. The rachises as well as the stems are covered with fine, reddish brown hairs, giving them a velvety appearance and providing a certain way to identify the plant. The form and fuzzy covering of the stems look like the antlers of a male deer or stag, thus, the common name.
Fall foliage is an unrivaled red in early in the season. Shades of orange and yellow can also be seen, and combined with red fruit clusters and interesting stem texture, this is a winning look for the landscape. Flower clusters are yellow-green in pyramidal panicles to 8 inches long, appearing in summer. In late summer the red, fuzzy fruits develop in dense clusters and are quite attractive. They remain upright and dense through the winter, but are eventually eaten by many kinds of birds.
Rhus typhina and a group of the cultivar ‘Dissecta’ were planted in the Longwood trials. ‘Dissecta’ is a cut-leaf form that was discovered in Massachusetts in 1892. (This cultivar is often erroneously called ‘Laciniata’.) The grouping of staghorn sumac failed to thrive after two years in the trials. It did not seem to suffer from any pest or pathogen problems, and no definite reason was given for the dieback and failure. ‘Dissecta’, on the other hand, came out with the highest average score of any Rhus evaluated. It averaged 3.1 for the entire length of the trials, and received many comments by delighted observers. The cultivar scored high at all times of the year, from spring through the winter. In the middle of November one year, it got the highest rating possible at 5.0. At the time, plants were defoliated and the score was based on the form, the stems and the seed clusters. It was said to have “stark architectural form” and was seen as dramatic. Comments about growth habit during the summer months described the plants as having a dense canopy with an “inviting shady area underneath.”
Though suckering was noted, people still loved the habit. Flowers and fruits were seen as positive attributes, and even old fruits were seen to add interest into March. Fruits were bold and interesting, and there was no getting around using the word “fuzzy” when describing the stems. When commenting on the stems, no one saw the texture as unappealing. The dissected leaves were called lacy, fine-textured and attractive. The pubescent, red rachis was also appreciated, and one person noticed in October that “the red-orange fall color draws attention from a long distance.”
Rhus michauxii (Michaux’s sumac) is a native sumac listed by the U.S. Fish and Wildlife Service as federally endangered. Its current distribution is listed as Georgia, North Carolina, South Carolina and Virginia, with each state only having a few counties containing populations. A smaller plant growing in open woods and disturbed areas, it has pinnately compound leaves; the rachis can be both winged near the apex and densely hairy; and the leaflets are coarsely toothed.
The antler-like architecture was one of the reasons Rhus glabra ‘Laciniata’ received high scores during the winter months.
A group of nursery-raised Michaux’s sumac started in the shrub trials at Longwood Gardens, but they never established well and did not survive past three years. It is important to state that no plants should be removed from the wild, whether federally endangered or not. This rare sumac is best left to its natural habitats and protected areas.
On the horizon
Some cultivars of native sumac worth mentioning were not included in the shrub trials at Longwood Gardens. More cultivars of sumac are becoming available in the trade that may work where you would not expect to find the species. One that is quickly catching on is a cultivar of R. typhina named ‘Bailtiger’ and sold as Tiger Eye®. Introduced by Bailey Nurseries, Newport, Minn., it derived from a mutation of ‘Dissecta’ and has intensely chartreuse, deeply cut leaves that turn yellow as the season unfolds. Described as a dwarf by some, it grows 6 feet tall and wide in full sun in zones 4 to 8. This cultivar can be grown in containers with vines like Clematis glaucophylla (whiteleaf leather flower) trained up its considerable stems.
A few cultivars of shining sumac also are available. Sold as Prairie Flame™, ‘Morton’ is a cultivar of R. copallinum introduced by the Morton Arboretum in Lisle, Ill. This selection retains all the desirable characteristics of the species – glossy, deep green summer foliage that turns bright red in autumn and showier, late-summer flowering panicles – but has a more compact size. It is said to grow no taller than 7 feet, and eventually spreads to about 10 feet. This may make it a more desirable shrub in smaller landscape plantings or for residential use. It is a fruitless clone selected from plants grown from seed collected near the Illinois/Indiana border.
Mike Creel of CreelWay Propagation in Lexington, S.C., has developed a cultivar named ‘Creel’s Quintet’. This is a female, fruiting variety similar in size to ‘Morton’ at 8 to 10 feet tall and wide. What’s unique about this selection is the number of leaflets per leaf: Each leaf has five leaflets rather than nine to 21.