Best of the Sweetshrubs: Plant Trial Results

With excellent foliage and few problems with pests or diseases, these nativars deserve more love

Woody plants take up a luck of space for a lot of years , so here at the Chicago Botanic Garden we must be choosy about which bush we judge . A sweetshrub test had been on our forgetful inclination for a while , so when some beds open up a few eld ago , I knew the time had descend . Eastern sweetshrub , otherwise known as Carolina allspice ( Calycanthusfloridus ) , is a morsel of a peculiar native , featuring deli­ciously fragrant maroon flowers in late spring on a suckering , multistemmed shrub . Cultivars have been selected for imperial leave , strong fragrance , and refreshing flower colour , which so far include creamy white , yellow , and red . Breeders have bring together our aboriginal — eastern sweetshrub and California sweetshrub ( C. occi­dentalis)—and an Asian mintage ( C. chinensis ) to create some hearty cultivar that offer up bigger flowers on larger plants .

At a glance

Calycanthusspp . and cvs .

zone : Eastern sweetshrub is wintertime hardy in Zones 4–9 but may support some dieback or accidental injury in the cold field . Thehybrids are considered less moth-eaten patient of , but all have been brave in our Zone 5 garden .

Conditions : Full sunlight to fond shade ; adaptable to a all-embracing range of soil types but prefers moist , well - run out territory ; kind ofalkaline pH

Native range : North America , Asia

Pests and disease : These shrubs have few pest or disease problem and are even deer insubordinate . seafarer staining on leaves and bloom can occur but is mostly cosmetic . The yellowish - putting surface to creamy - white flower of ‘ Athens ’ and ‘ Venus ’ were more prone to old salt spotting than those of maroon - bloom cultivars .

|Trial Parameters|

Since 2018 , the Chicago Botanic Garden has evaluated 13 unlike sweetshrubs in comparative trial . insensate hardiness , especially have-to doe with to the hybrid cultivar , was a focusing of our trial .

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A fragrant floral display makes them noteworthy

When I take on the curious brownish - reddened flowers of eastern sweetshrub for the first time , they seemed like something only a fly or beetle would appreciate . Imagine my surprisal when the fragrance was like Juicy Fruit mucilage and not carrion . Over the years , my evaluators have described the flowered scents of sweetshrubs as umber - Ceylon cinnamon tree - licorice , apple , plum , musk melon , cranberry , combust sugar , liquid ecstasy , sweet Berry , and umami . Fragrance is subjective and personal , and it may cross-file as intemperate , pernicious , or altogether subtle to dissimilar people . However , we agreed that eastern sweetshrub selections more often than not have a unattackable odour than the hybrids , and that ardent temperatures can intensify the fragrance .

Sweetshrub flowers could be describe as resembling magnolia or Indian lotus flowers in shape , with strappy tepal ( petals and sepal that see the same ) that unfurl step by step from plump ellipse buds . The independent efflorescence show is on older stems in late springtime , with sporadic flowering on fresh growth hap in midsummer .

Fall colour . Photo : good manners of Richard Hawke

Fruit pod . Photo : Danielle Sherry

Interesting fruit and foliage extend the seasonal interest

The leathery , veiny fruits that evolve after flowering are a wonder but are not especially ornamental . These pendulous , urn - shapedpods are 2 to 3 inches longand resemble purse figs or funky chrysalis . They ripen to brown over winterand often persist on industrial plant well into summertime . Bruised or crushed leaves release a spicy , fruity perfume . Yellow to golden - yellow pin foliage color is common but can vary wide . For lesson , by Halloween 2022 ‘ Edith Wilder ’ was uniformly brilliant golden - yellowed ( exposure top left ) , while ‘ Venus ’ was still mostly green .

‘ Aphrodite’(C.‘Aphrodite ’ , Zones 5–9 ) is undeniably a Samson , grownup than other cultivars by almost every measure . cherry-red - purple flowers up to 4 inches wide overt to disclose creamy yellow marker on the innermost tepal . The flowers are held on longer still hunt , so they are less masked by the leaves . ‘ Aphrodite ’ resembles ‘ Hartlage Wine ’ , but it flower about two weeks later . More - refined noses reek plum tree and spice in the lighter , fruity fragrance , but the scent elude me completely . The lush green leaves , tinged with bronze early in the time of year , are among the long of any sweetshrub ’s . Fall colour comes on late , turning from a mix of bright yellow and green to fat golden - yellow before the leaves drop . At 9 foot tall and 13 feet encompassing , ‘ Aphrodite ’ was a behemoth , even overshadow ‘ Hartlage Wine ’ , which is also pretty big . The robust , bushy plant once in a while appeared a little unruly or crazy because of long , vigorous stems , which were notable on young plants or latterly in the season . Cold validity has not been an military issue here , despite the fact that California sweetshrub is part of its familial make-up .

‘ Hartlage Wine’(C.×raulstonii‘Hartlage Wine ’ , Zones 5–9 ) is a loanblend that uprise at North Carolina State University’sJC Raulston Arboretum in 1991.Like the other intercrossed culti­vars , ‘ Hartlage Wine ’ has lavish foliage , a vigorous and full-bodied riding habit , and heavy blossom product from belated bound to midsummer . It ’s advert for my Quaker Richard Hartlage , who made the original cross when he was a college student . The 3 - column inch prime emerge burgundy - Red River and fade to a soft puce color , with near - whitened inner tepals and a light , fruity fragrance . The dense , bushy flora benefit from episodic Christ Within pruning to keep contrary stems in check . In pin the leave of absence turn deep chickenhearted but shake off quickly , even while the remaining foliage is still green .

Roy ’s Dark Red ™ (C. floridus‘KLMY ’ , Zones 4–9 ) has midwestern roots , having been pick out in southerly Wisconsin by acclaimed gardener Roy Klehm . It fall shortsighted of top sucker in our trial but is deserving of an honorable mention . While more maroon than red , the flowers have a slim silvery sheen and are quite dark compared to other natural selection . On most day , I found Roy ’s Dark Red ™ to have a heavy , sweet fragrance ; warm temperatures enhance the scent , but sometimes there was barely a hint . The 2 - inch blossom are so dark that they can be well overlooked in the axil of the lustrous dark green leaf . Some foliar chlorosis on older foliation take away from the healthy glow of the lustrous new leaves . The free fall colour is dirty yellow with a brownish dramatis personae , which makes the plants look a minuscule rough overall . At less than 5 understructure tall , Roy ’s Dark Red ™ is one of the forgetful cultivars , but its summary habit was less obvious by the fifth year , when suckers had fill the space between industrial plant .

Richard’s Favorite Sweetshrub

A few geezerhood ago , I was call for to do a smell check on’Michael Lindsey’(C. floridus‘Michael Lindsey ’ , Zones 4b–9 ) . I thoughtat the time that it had the unspoiled fruity fragrance of any of the plants in the visitation . Its benighted maroon flowers are among the smallest — just a shade larger than those of the metal money — and arefreely get in late spring . The showy folio are of a noticeably darker green than those of other cultivars , and in fall they ferment a beautiful lustrous jaundiced with gold tones . ‘ Michael Lindsey ’ suckers like the specie and spring a well - balance rounded ­habit , second only toC. floridusvar.glaucus‘Purpureus ’ in quality . The suckering nature amplifies the plant ’s girth — it grows more than 8 feet wide and 6 foot improbable . ‘ Michael Lindsey ’ is an older cultivar , selected and introduced by plantsman Allen Bush .

|How - to|

Pruning 101

Pruning sweetshrubs is seldom necessary , but when it is take there are a few point to keep in judgement . Sweetshrubs bloom on sure-enough wood ( the previous class ’s ontogeny ) as well as on new wood , so removing old stems in winter or spring will reduce the early flower show . Pruning — again , only if needed — is loosely best done in summertime , after flowering . If the plant has gotten too large or is a bit unruly , pruning to reshape and to control size of it is best done after flower too .

There are a few elision to the summertime pruning rule :

1.A little formation in fountain is fine . To even out an unbalanced habit , you may take to take out a few obstinate or overly vigorous branches in spring .

2.If it ’s dead , timing is n’t significant . Winter - injured or dead branches can be ­removed at any time to better the appearance of the shrub .

3.Remove suckers right aside . Due to its suckering nature , eastern sweetshrub forms thickets over time . To reduce the shrub ’s width and keep things sizeable , take out sucker as they emerge .

A note on hybrids

interspecies loan-blend have change the face of sweetshrubs forever . The first sweetshrub hybrid resulted from cross made in 1991 by Richard Hartlage when he was a student at North Carolina State Univer­sity ( NCSU ) . One of the original seedlings come along to be a hybrid betweenSinocalycanthus chinensisandCalycanthus floridusand was give the clapper - twisting botanic name× Sinocalycalycanthus raulstoniito distinguish its intergeneric origin as well as to recognize J. C. Raulston , professor and botanical garden director at NCSU at the clip .

My memories of the subsequent year were of a lot of discussion and hand - wringing to iron out the terminology . When that was all done , taxonomists had movedSinocalycanthusintoCalycanthus , downgrading the cross from intergeneric to interspecific . They settled onCalycanthus × raulstoniito describe theC. floridus × C. chinensis(néeSinocalycanthus chinensis ) cross , and reward Richard ’s original knockoff as ‘ Hartlage wine-coloured ’ . Tom Ranney , an clever plant breeder at NCSU , followed up with two more exceptional hybrids in the former 2000s . ‘ Aphrodite ’ is a cross betweenC. chin­ensisandC. occidentalis , and clean - flowered ‘ Venus ’ is a complex hybrid cross ofC. chinensis , C. floridus‘Athens’,andC. occidentalis . ‘Solar Flare ’ and ‘ Dark Secret ’ are more recent intercrossed introduction with the same American and Chinese parentage as ‘ Hartlage vino ’ .

• Sweetshrub trial results •

Rating

Calycanthus

Height

Width

Flower Color

Flower Diameter

Fall color.Photo: courtesy of Richard Hawke

Leaf Size(Length × Width )

C.‘Aphrodite ’

108 in .

Fall color.Photo: courtesy of Richard Hawke

156 in .

carmine purple , creamy yellow

4 in .

Fruit pod.Photo: Danielle Sherry

7½ × 3½ in .

C.‘Venus ’

66 in .

‘Aphrodite’.Photo: Danielle Sherry

118 in .

creamy clean , blushful blush

3 in .

’Hartlage Wine’.Photo: Danielle Sherry

4¾ × 3 in .

C. floridus

72 in .

Roy’s Dark Red™.Photo: Danielle Sherry

103 in . *

maroon

1½ in .

‘Michael Lindsey’.Photo: Danielle Sherry

4½ × 2 in .

C. floridus ‘ Athens ’

86 in .

Illustration: Jessica Daigle

light yellow fleeceable

2 in .

C. floridus‘Burgundy Spice ’

Photos: courtesy of Missouri Botanical Garden Center (left); Michelle Gervais (center); Danielle Sherry (right)

48 in .

64 in .

1¾ in .

Photos, clockwise from top left: courtesy of Missouri Botanical Garden (2); courtesy of Thomas Ranney (2) Danielle Sherry

6 × 3½ in .

C. floridus‘Edith Wilder ’

59 in .

70 in .

4½ × 3 in .

C. floridus‘KLMY ’ Roy ’s Dark Red ™

57 in .

82 in .

dark maroon

6 × 2¼ in .

C. floridus‘Michael Lindsey ’

100 in . *

5 × 2½ in .

C. floridusvar.glaucus‘Purpureus ’

50 in .

104 in . *

C.×raulstonii‘Dark confidential ’

78 in .

81 in .

dark burgundy , creamy blank

7 × 4¾ in .

C.×raulstonii‘Hartlage Wine ’

90 in .

103 in .

burgundy - red , clean

7 × 4½ in .

C. ×raulstonii‘Solar Flare ’

85 in .

89 in .

mauve - puce , yellowish

2½ in .

7¾ × 4¾ in .

• forecast breadth due to suckering habit

[ KEY ]

★ ★ ★ ★ fantabulous

★ ★ ★ Good

★ ★ Fair

★ pitiful

NRNot rated(new to trial )

Richard Hawke is an expert horticulturist and the conductor of ornamental flora research at the Chicago Botanic Garden in Glencoe , Illinois .

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