The unusual groundsel-bush stages a striking autumn display.
The rich, purplish-red color on the base of the fruits is another attractive feature.
Baccharis halimifolia, commonly referred to as groundsel-bush or salt-bush, is rarely seen in today’s cultivated landscape. Perhaps unjustly accused of a lack of refinement and scruffy appearance, this native shrub from the family Asteraceae possesses a number of ornamental attributes that lend themselves to judicial landscape use. Among these are adaptability to a wide range of soils and climates, ease of propagation, prolific late-season flowers that are highly attractive to bees and butterflies, and a stunning display of feathery fruit in autumn. Another characteristic of groundsel-bush is its avoidance of deer browsing, an important consideration in suburban environments. Within its native range, groundsel-bush represents an unexploited opportunity for wider utilization and the development of exciting and sustainable landscape plants.
Variable leaf size and shape is evident on Baccharis halimifolia ‘White Caps’.
PHOTOS COURTESY OF BARRETT C. WILSON, LONGWOOD GARDENS
A wild past and present
Historically found in the outermost Coastal Plain areas of the eastern U.S., groundsel-bush is now spread broadly inland, partly due to human influences on the landscape. The current range is from Coastal Plain and Piedmont areas of the eastern and southern U.S., spreading west to Texas and Oklahoma. At its limits, groundsel-bush even grows in extreme southeastern Canada and northern Mexico, encompassing USDA hardiness zones 4 to 11. The common name of salt-bush is well-earned, as it thrives along roads subjected to heavy salt applications in winter. Both acidic and somewhat alkaline soils are tolerated, along with a diverse array of soil types, nutrient availabilities and moisture levels.
A deciduous and dioecious (with male and female flowers on separate plants) large shrub or small tree, groundsel-bush can achieve heights up to 13 feet at maturity. Individual specimens tend to be clumps of multiple stems or trunks, but can be trained to have a single primary stem. The alternate leaves are coarsely serrate and elliptic to obovate in shape. Leaf size is variable but can be up to 2.5 inches long and 1.5 inches wide, with petioles around 0.25 to 0.5 inch long.
Flowering occurs from September through October, with fruiting soon afterwards. The flowers of male shrubs are rich in nectar, which attracts bees and butterflies. Female flowers are consequently insect-pollinated. The peduncled, whitish flower heads are solitary or arranged in clusters of three to four at the tips of stems. Each flower head is composed of individual flowers, or florets. Both male and female flower heads are composed of 20 to 30 florets. The fruits are cylindrical achenes less than half the length of a rice grain. These achenes are decorated with striking, feathery pappus around 0.25 to 0.5 inch long. The prominent white pappus on the mature fruits of female plants are readily seen in abandoned fields, clearings, highway edges, and other open areas receiving full sun.
The white fluffy pappus is an appealing feature on female plants of Baccharis halimifolia.
The seeds have no dormancy requirement, have a high germination percentage, and are tolerant of shade. This, along with long-range wind dispersal of seed aided by the pappus, has led to groundsel-bush being classified as invasive in some regions outside North America, where it was introduced. It is particularly detrimental in eastern Australia and Mediterranean Europe. Established plants can also re-sprout from fire and severe cut-back, making them difficult to eradicate.
A rare visitor to the cultivated landscape
Because of its natural habit, groundsel-bush is probably best used in informal screens or mass border plantings. If a single specimen is desired, regular thinning and removal of dead branches may help to form a small tree. Pruning should ideally be done immediately after flowering. The expected lifespan of groundsel-bush is up to 50 years, and it can therefore crowd out under-planted species over time. Groundsel-bush would also be ideal to use in locations with high deer populations. The leaves and flowers contain cardioactive glycosides, making them unpalatable and toxic to both deer and livestock. Potential minor pests of groundsel- bush are green scale (Coccus viridis), white scale (Pinnaspis strachanii), leaf beetles (Trirhabda baccharidis) and several types of sooty mold. These have not been serious enough to cause concern in cultivation.
A shrub border of Baccharis halimifolia in early fall.
Groundsel-bush on trial
The extensive Longwood Gardens shrub trials began in 1997 on a 7-acre site in Kennett Square, PA. At its peak, testing comprised more than 1,300 taxa monitored for size, growth habit, foliage interest, flowering, environmental injury, pest/pathogen resistance, and overall aesthetic appeal. The evaluation team consisted of professional horticulturists and researchers, students and volunteers who rated the criteria at different times throughout the year. These subjective ratings were based on a scale of 1 to 5 (1 = unattractive, 2 = acceptable, 3 = attractive, 4 = very attractive, 5 = best in class). Four selections of groundsel-bush were evaluated at various dates from 1997 through 2006. Three specimens of each selection were planted in full sun and received only minimal maintenance during the trial. Irrigation was withheld after the first year, and mulching, weeding and pruning occurred on an as-needed basis.
The first groundsel-bush planted in the trials was an unnamed offering from Woodlanders Nursery (Aiken, S.C.). Reaching 7 to 8 feet in height after six years, this selection was upright and dense, exhibiting an oval to rounded form. There was one report of minor wind damage in March of one year. Evaluators pegged its habit as “billowy and airy” and “upright and bushy.” New growth was green, and stems were striped or striated with gray and red-brown streaks. Evaluators were pleased with the “attractive stripey bark” and the winter interest it provided.
Some specimens have paler colors on the base of the fruit.
In contrast, the summer foliage display was underwhelming. The small, lanceolate leaves were densely arranged at branch tips and showed much variation in serration and lobing. Color ranged from light to dark green, changing to a mix of light green, brown and yellow during autumn. Small white flowers appeared in large clusters swarming with bees, with white fluffy seed heads appearing in October and November. According to one evaluator, the pappus was like “tiny dandelions.” The overall rating from late winter through spring was an unattractive 1.3. Rating for the summer and fall display was a moderately attractive 3.
One of the few named cultivars of groundsel-bush in the trial was B. halimifolia ‘White Caps’, selected by Kurt Bluemel of Bluemel Nursery (Baldwin, Md.). ‘White Caps’ achieved a size of 10 feet by 10 feet over an eight-year period. The habit was described as being finely branched and smaller than the species type. Overall, the habit of ‘White Caps’ was uniform, dense and rounded. Stems exhibited attractive green new growth and a textured, striped gray-brown bark. Foliage was tough and glossy with variably entire margins. New growth was lime green, changing to a yellowish brown-green in fall. Flowers buds were clustered on branch tips, a light creamy yellow-green or chartreuse.
In October, the plants appeared to be completely covered in showy white pappus. As far as pest and disease concerns, there was occasional powdery mildew and minor insect leaf damage, but this did not detract from the overall appearance. ‘White Caps’ maintained an acceptable winter-spring rating of 2, while the summer-fall rating was a more attractive 2.9.
Baccharis halimifolia ‘Select’ was an introduction from the now-defunct Roslyn Nursery (Dix Hills, N.Y.). A more vigorous grower than the others, ‘Select’ reached a size of 15 feet by 10 feet after just five years in the field. Its habit was upright, but open or “see-through” in the center. Significant tip dieback was noted in the third and sixth years of trialing. Bark was reddish-brown with new green growth striped with red. The small, gray-green leaves were narrower at the tops and had a shiny, sandpaper-like surface. The degree of lobing on the leaves was quite variable. Tiny light green flower buds, clustered at branch tips, pleasantly covered the entire shrub.
As with the other varieties, the fruiting display was the primary allure, covering the entire plant like a white cloud. The only notable pest damage was from caterpillars covering roughly 30 percent of the leaf area in late summer of one year. Leaf miner and powdery mildew were minor annoyances. ‘Select’ was rated similarly to the others, around 2 for winter-spring and 2.9 for summer-fall.
The final groundsel-bush in the trial was wild-collected in Ocean County, New Jersey, by Reeseville Ridge Nursery (Reeseville, Wis.). This unnamed selection achieved 8 feet by 8 feet after four years in the field. The habit tended to be more compact, dense and rounded, described by some evaluators as an upright mound. Stems and twigs were dark brown with tan-orange recesses. Foliage was a light grayish-green, somewhat glossy and serrated at the apex. Flower bud set was quite heavy, resulting in a fine fruiting display by October. The base of the seed head had a richer red color compared to typical specimens. Ratings averaged 2.3 for the winter and spring seasons and 2.8 for summer and fall. The higher scores for winter and spring may be attributed to the juvenility of the plants, which were only in the field for four years. Most dieback and breakage tended to occur with more than five years of field testing.
The family tree
The genus Baccharis comprises about 25 species within the family Asteraceae. Other species besides B. halimifolia present in the shrub trials were B. angustifolia and B. glomeruliflora from southeastern U.S., and B. pilularis from drier areas of California, Oregon and Baja California. All failed to survive three years, presumably due to severe winter dieback or excessive soil moisture. Species not trialed but sometimes available in the nursery trade are B. dioica (Florida and Puerto Rico), B. gilliesii (Argentina and Bolivia), B. magellanica (Argentina and Chile), and B. sarothroides (desert Southwest).
As mentioned previously, groundsel-bush has many characteristics suitable for further refinement. Among the most important of these are: extending flowering and fruiting duration, developing seed sterility and improving cold hardiness. In our trials, the area needing improvement most appears to be the foliage, particularly during summer. Groundsel-bush is often unseen in the landscape until fall, when the fruit seem to pop out of nowhere. Improvement of foliage characteristics (for example, glossiness, thickness, color) could potentially enhance the summer display and, consequently, increase the overall value of the shrub.
Another concern is that of unwanted seed dispersal. This is the primary modality for its invasive colonization of introduced areas. In developing new cultivars, seed sterility would be a highly desirable trait. Increased seed retention on the shrub could potentially mitigate the extent of aggressive spreading throughout a planted landscape.
This wild-collected Baccharis halimifolia has a compact, rounded form.
A review of woody plant references and nursery inventories revealed just a few named cultivars other than ‘Select’ and ‘White Caps’. B. halimifolia ‘Orient Point’, a 1999 introduction from Fairweather Gardens (Greenwich, N.J.), purportedly has a much redder color at the base of the fruit. Kolster B.V., a nursery and production facility in the Netherlands, has patented three B. halimifolia: ‘Kolmmyst’ (Magical Mystery), ‘Kolmsil’ (Magical Silver) and ‘Kolmstar’ (Magical Star). Targeted to the cut-flower industry, these three cultivars are noted for their earlier flowering and are purported to be hardy to -5 ˚F.
Early development and selection of groundsel-bush have not yet yielded an impressive array of cultivars. Current choices are probably best paired to a niche use, such a native plantings or wild borders. The door is open for new cultivars suitable for a more prominent presentation in the home landscape. Nurserymen and other horticultural enthusiasts should keep an eye out for local Baccharis populations. Both phenotypic and genotypic variability are likely to be high due to its widespread distribution throughout eastern North America. As past experiences teach, when keen plantspeople scout through natural areas and pay attention to the diversity within populations, new and improved selections are bound to happen.
Barrett C. Wilson is research assistant in the research and production department at Longwood Gardens, Kennett Square, Pa. Dr. Tomasz Anis´ko is the curator of plants for Longwood. Wilson can be reached at email@example.com; Dr. Anis´ko can be reached at firstname.lastname@example.org.