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The 91����Ƶ’s first hardy hibiscus trial ran from 1989 through 1992 and featured 29 cultivars that were in the marketplace at the time. The recently completed trial of 47 taxa occurred from 2009 through 2024; the trial included contemporary cultivars introduced during that timeframe. Breeding trends leading up to and during the recent trial period were the impetus for undertaking the new study. Many of the earliest cultivars were tall and flowered only at the tops of the plants, while more recent breeding and selection has developed shorter cultivars with increased floriferousness and extended bloom periods. A full list of the hardy hibiscus cultivars evaluated between 1989 and 2025 is shown in Appendix 1.

Each taxon was evaluated for four years, although some hibiscuses remained in the trial garden for up to eight years [see Appendix 1]. A minimum of three plants of each taxon were grown side-by-side for easy comparison of ornamental traits and landscape performance. The evaluation garden was openly exposed to wind in all directions and potentially received up to 10 hours of full sun daily prior to 2015.

Maturing sycamore trees in an adjacent landscape eventually cast significant shade over portions of the trial bed from 2015 onward. In recent years, a portion of the plants were only in full sun until early afternoon. The clay-loam soil had a pH of 7.4, and although typically well-drained, the site occasionally retained excess water for short periods in all seasons.

Maintenance practices were kept to a minimum, thereby allowing the plants to thrive or fail under natural conditions. Trial beds were irrigated via overhead sprinklers as needed, mulched with composted leaves once each summer, and regularly weeded. Moreover, plants were not deadheaded, fertilized, winter mulched, or chemically treated for insects or diseases. All stems were cut back to short stubs in late winter to mark the location of the late-emerging shoots. Emergence typically occurred in late May to early June.

Shoots emerging among winter stubs

Thirteen taxa received four-star excellent ratings for their overall ornamental display related to strong flower production, foliar and habit quality, and ease of culture.

Plants were generally cold-hardy in our Zone 5b/6a site, so winter injury was not a primary factor in the final ratings. The four-star hardy hibiscus included ‘Berry Awesome’, ‘B���������������dzܲ�’, ‘Cranberry Crush’, ‘Dark Mystery’, ‘Evening Rose’, HEAD OVER HEELS^® Adore ['RutHib3'], ‘H�𲹰��ٳٳ���Dz�’, ‘Mars Madness’, ‘Midnight Marvel, 'Mocha Moon', "Perfect Storm', 'Sultry Kiss', and 'Vintage Wine'.

Hibiscus ‘Berry Awesome’ 

Years trialed: 2016 – 2021

‘Berry Awesome’ had 8-inch magenta flowers with a dark red eye. Flowers were freely produced and evenly distributed on the plant from late July to early September and were generally self-cleaning, i.e. falling freely to the ground. The dark green and burgundy dissected leaves had a unique silvery cast. ‘Berry Awesome’ had a uniform bushy habit to 52 inches tall and 69 inches wide with attractive purple-red stems.

 

Hibiscus ‘B���������������dzܲ�’

Years trialed: 2012 – 2016

The light pink-purple flowers of ‘B���������������dzܲ�’ were bountiful from late July to mid-September. The nearly flat, 8-inch blossoms featured ruffled petals and a bright red eye. Flowers were borne all over the dense bushy plants—50 inches tall and 60 inches wide. ‘B���������������dzܲ�’ was consistently recorded as having one of the best overall habits. Its bright green dissected leaves were attractive all summer, although minor cosmetic damage from flea beetles was observed periodically. Unfortunately, spent flowers hung onto the plants longer (and more consistently) than on most other cultivars and was exacerbated in wet weather.

 

Hibiscus ‘Cranberry Crush’

Years trialed: 2013 – 2017

The 8-inch flowers of ‘Cranberry Crush’ were deep scarlet-red—the color so intense that the red eye was barely discernible at the center of the slightly cupped petals. The color intensity was heightened as the dark blood-red flower buds ballooned before opening in late July. The dissected leaves were shiny deep bronze early on but turned dark green with purple overtones for the summer. ‘Cranberry Crush’ bloomed fully over dense rounded plants—50 inches tall and 56 inches wide— and consistently received high marks for habit uniformity.

Hibiscus ‘Dark Mystery’

Years trialed: 2020 – 2024

The oval leaves of ‘Dark Mystery’ were among the darkest in the trial— rich burgundy with a chocolatey tone that set it apart from other dark-colored selections such as ‘Midnight Marvel’ and ‘Perfect Storm’. The cherry red eye bled along the veins in a starburst pattern, giving the white flower a pink blush. The 8-inch blossoms were produced freely from mid-August to mid-September. ‘Dark Mystery’ was consistently noted as one of the best displays of the year due to its dark foliage, prolific bloom, and robust habits to 52 inches tall and 53 inches wide. Flea beetles were observed on the plants in most years, but the damage was deemed a minor cosmetic issue.

 

Hibiscus ‘Evening Rose’

Years trialed: 2019 – 2023

‘ ‘Evening Rose’ featured 8-inch, hot magenta-pink flowers with red eyes. The petals were prominently puckered or ruffled and shallowly cupped. Strong burgundy dissected leaves paired nicely with the bright flowers. Leaf color was not as consistent as ‘Dark Mystery’; green leaves were part of the color mix when flowers started blooming in early August. Although flowering typically ended in mid-September, a second minor bloom was occasionally noted in October. Plants had rounded, bushy habits to 53 inches tall and 56 inches wide.

 

Hibiscus moscheutos HEAD OVER HEELS^® Adore

Years trialed: 2020 – 2024

The texture of its oval leaves set HEAD OVER HEELS^® Adore ['RutHib3'] apart from most other cultivars. The green and burgundy leaves were covered in soft stellate pubescence, which gave them a silvery velvet appearance, especially lustrous in bright sunlight. The pubescence comes from one of its parents H. moscheutos ssp. lasiocarpos. Pink, 8-inch flowers were evenly distributed over the entire bushy plants from early August to mid-September. Although flea beetles were observed on the plants, minimal foliar damage was noted. Plant habits were full and robust, 60 inches tall and 70 inches wide.

Hibiscus ‘H�𲹰��ٳٳ���Dz�’

Years trialed: 2013 – 2019

From nearly black buds, ‘H�𲹰��ٳٳ���Dz�’ opened to deep blood red flowers with darker black-red eyes. The 9-inch-wide flowers were generously produced from late July to mid-September and were well-distributed over the entirety of the 5-foot-tall bushy plants. A touch of bronze was present on the large oval leaves in spring, but the leaves quickly turned green with green stems in summer.

 

Hibiscus ‘Mars Madness’

Years trialed: 2016 – 2021

From early August to mid-September, ‘Mars Madness’ produced an abundance of 9-inch-wide deep red flowers with slightly darker red eyes and overlapping, crinkled petals. The large lobed leaves were distinctly burgundy in spring, fading to dark coppery green for the summer. ‘Mars Madness’ had one of the most substantial habits at 57 inches tall and 80 inches wide.

 

Hibiscus ‘Midnight Marvel’

Years trialed: 2013 – 2021

From late July to mid-September, the dark burgundy leaves of ‘Midnight Marvel’ were liberally dotted with deep scarlet-red flowers. The slightly cupped 8-inch flowers were as vibrant as ‘Cranberry Crush’, while the large, dissected leaves were as dark as ‘Summer Storm’. The leaf color held for most of the season but dimmed to bronze-purple in midsummer before turning half purple, half green in September—the base of each leaf was yellow-green throughout. ‘Midnight Marvel’ had dark purple-red stems and a uniformly robust bushy habit to 56 inches tall and 58 inches wide.

Hibiscus ‘Mocha Moon’

Years trialed: 2016 – 2021

The huge white flowers of ‘Mocha Moon’ to 8-9 inches wide—featured bright red eyes that bled vividly into the broad overlapping petals. Its deep bronze-green dissected leaves were held on dark purple-red stems. The bright lime green spidery floral bracts contrasted nicely against the bronze foliage during and after blooming. ‘Mocha Moon’ had a bushy habit to nearly 5 feet tall and 6 feet wide.

 

Hibiscus ‘Perfect Storm’

Years trialed: 2015-2021

The pink-blushed white flowers of ‘Perfect Storm’ looked pink from afar. The slightly cupped 8-inch flowers had an especially large, vivid deep red eye at the base of the overlapping petals. The dark burgundy dissected leaves were exceptionally colorful but were mixed with green later in the season. At 4 feet tall and 6 feet wide, ‘Perfect Storm’ had a full bushy habit.

 

Hibiscus ‘Sultry Kiss’

Years trialed: 2010 – 2016

The floral show of ‘Sultry Kiss’ was a standout in the trial. Deep red buds opened to 10-inch-wide magenta-red flowers with overlapping petals. Flowers were profusely produced from late July to mid-September. Dark green dissected leaves featured a bronze to purple cast early in the season—the uppermost leaves were purple-blushed in midsummer. ‘Sultry Kiss’ had a robust bushy habit reaching 5 feet tall and wide.

Significant breeding developments related to flower production, foliar traits, and plant size have occurred since the 91����Ƶ’s original hardy hibiscus trial in 1989. Perhaps most noteworthy is the development of indeterminate blooming, where both terminal and axillary flowers are produced, resulting in increased bloom production over more of the plant and a prolonged bloom period. Flower coverage and peak floral displays were not easily measured on the hardy hibiscuses due to the single-day lifespan of an individual flower and the random opening of new flowers daily over the long flowering cycle. Conversely, flower production was generally high on all hibiscuses and increased correspondingly with age as the number of stems per plant increased.

The shapes and colors of hardy hibiscus leaves have also changed significantly from the cultivars in the earlier trial. Oval [ovate to heart-shaped] leaves were predominant on older selections, whereas the leaves of modern hybrid cultivars are more commonly lobed [oval with shallow lobes] or dissected [deeply divided or incised]. Furthermore, cultivars with burgundy or bronze leaves are now more prevalent too. Only three of the 29 cultivars—about 10 percent—in the 1989 trial exhibited some reddish coloration on dissected leaves. The final report on this trial noted that “red petioles, veins, and leaf margins were most prominent on 'Anna J. Hemming' and 'Red Cutleaf', and less so on 'Lord Baltimore’. The intensity of red was deepest as the leaves emerged and markedly dissipated as the season progressed. These three cultivars were also the only plants with dissected leaves”. Conversely, 31 taxa or almost 70 percent of the cultivars in the current trial had dissected leaves—of these, 55 percent were green, while 45 percent were partially to fully burgundy or bronze. And nine cultivars in the trial held the dark burgundy foliage color throughout the growing season.

Most cultivars were spindly-stemmed in the first year or two in the ground. By the third year, the hibiscuses generally had bushy multi-stemmed habits. Consistently loose, open, or uneven habits during the trial period factored into lower overall ratings for several cultivars such as ‘Dave Fleming’, ‘Robert Fleming’, and the SUMMER SPICE^® series— CRÈME DE LA CRÈME^™, RASPBERRY FLAMBE^™, and VINCOTTO^™.

The hibiscuses were generally adaptable to the clay soil of the trial garden. The periodic and sometimes protracted wetness of the site was not problematic for established hibiscus. However, fluctuations in soil moisture from wet to dry occasionally caused small plants to struggle during their first year. Plants in one-gallon production pots were most common at planting; however, occasionally a few smaller and weaker plants in 4-inch pots were planted, resulting in less successful establishment in year one and sometimes into the second year too. A grove of sycamore trees planted near the hibiscus plot in 2012 gradually created more shade on the hibiscus as the trees grew taller. Sun exposure began gradually decreasing in 2015, eventually averaging about four hours per day for half the plants by 2025. The increased shade adversely impacted habit quality, resulting in stretching and openness on some plants.

Most taxa fully survived all winters during the trial. However, several exceptions were noted: all plants of ‘Stardust’ suffered 50-80% crown loss in 2012, two plants died in 2013, and one plant died in 2015; one plant of ‘Strawberry Swirl’ died in 2012 and minor crown injury on all remaining plants was noted in all years of its trial; all plants of ‘My Valentine’ died during the final winter of its trial (2016); and one plant each of RASPBERRY GLACE™ (2024), VINCOTTO™ (2022), and ‘Tie Dye’ (2013) died during their respective winters.

The hibiscuses were disease-free during the trial periods, but damage from Japanese beetles and flea beetles was commonly observed. Shotholes caused by one or both beetles feeding on the leaves were considered cosmetic, which impacted the habit quality rating rather than plant health. Flea beetles were more commonly observed on the hibiscus than were Japanese beetles, likely in part due to local populations of Japanese beetles declining over the last ten years. Beetle damage varied by year and by degree, from minor to severe— in severe cases leaves and flowers were occasionally skeletonized. Hibiscus sawfly was not observed in the trials.