All About Sweetshrub: Calycanthus Species, Cultivars and Hybrids
The rundown on choosing and growing sweetshrub.
Most American gardeners know Calycanthus only from its most common species, C. floridus, which goes by the common names of sweetshrub or Carolina allspice, among a few others. This Southeast native ranges from New York to Florida and west to the Mississippi River region, where it forms a rather large shrub to about eight feet tall and wide, most often on moist, light understory sites.
From an ornamental standpoint the species can fill a nice range of landscape niches. It offers dependable, high-quality, medium to dark green leaves all summer. Held opposite, these are densely wooly on the underside and they suffer few chewers throughout the season. Fall color is a bright and clear yellow.
Sweetshrub’s late-spring blooms span up to two inches and fall into a rather difficult-to-describe color; it’s been called mahogany, brown or, by those looking to sell rather than accurately portray, red. Plant nerd detail: Calycanthus bear no distinct petals. Their sepals and petals are fused into what are called tepals.
If you’re in for a good time, fill a room with plant dweebs and ask each to describe the fragrance of C. floridus flowers. All will agree that it varies quite a bit from one plant to the next, from flower to flower on one plant and from morning until evening. But that’s about where the consensus ends. The scent is strawberry, green apple—I even had one group of University of Maine woody-plant students concur that it smelled like that crunchy white paste used (still?) by kindergarteners across the land. Bruised bark and roots smell of camphor or, by that same class of college students, gin and tonic.
Finally, the fruit offers not much in the ornamental realm, but they do provide a serious bailout for students of woody plant ID. The two- to three-inch-long capsules look a bit like squashed lotus, with a leathery, becoming quite hard, texture and a single opening at the tip. Up to half a dozen pea-size seeds usually remain in the capsule most of the winter. There are rumors that green but mature seed will germinate without pretreatment, but I’ve never had any luck. The standard three months of cold, moist stratification usually does the trick.
Culturally, Carolina allspice is a gardener’s dream. Perfectly happy in full sun to filtered or even relatively deep shade, tolerant of a wide range of soils and susceptible to few pest problems, it’s just a doer. It’s easily propagated by separating off root suckers, so you can always make more to share. It grows well from Florida to Massachusetts and, with a little occasional tip dieback, all the way up to coastal Maine. I’ve seen it growing well in Denver, Colo., Madison, Wisc., and Tulsa, Okla.
Other Species
Historically there have been a couple of other minor species in the same geographic range separated out by taxonomists, but most (C. fertilis and C. mohrii) are now considered to fall within the range of C. floridus.
Unbeknownst to most Eastern and Midwest American gardeners there is also a West Coast species, C. occidentalis. Rarely grown outside its native haunts (and not grown all that much there, either), the common sweetshrub grows a bit larger and can be a tad unruly. It will grow up to 12 or 15 feet tall, with a slightly larger flower that tends closer to actual red.
Then there’s C. chinensis—the Chinese sweetshrub, or wax flower. It was virtually unknown in the United States until the 1980s, The late J.C. Raulston of North Carolina State University was the first one to grow and flower this plant in the States. With white, non-fragrant flowers in late spring and early summer, this is an absolute beast of a grower. Leaves grow eight to ten inches long, offer little useful fall color and actually get quite tired looking in late summer. In my garden I’ve taken to whacking this plant to the ground in early July, after the bloom display ceases. It then puts on about five or six feet of growth and sets flower buds before the end of the growing season. Not a technique you’ll find in many how-to books, but it does the trick and keeps the size manageable.
But the magic in Calycanthus in the garden has come not from these straight species but from fabulous selections and crosses.
Favorite Sweetshrub Selections
Calycanthus floridus cultivars
:
‘Athens’. No list would be complete without this Mike Dirr–named beauty. It’s a touch smaller than the straight species, and its real standout attribute is the yellow-chartreuse color of the blooms. Nice fragrance in bloom and good yellow fall foliage color.
‘Michael Lindsey’. Hands down best form for a straight species selection. It has deep green, sharply pointed leaves that remain glossy all through the summer then turn a glowing golden color. And the flowers are as fragrant as any other. Named and introduced by my Louisville, Ky., gardening friend Allen Bush.
‘Edith Wilder’. This is a larger than average grower with excellent floral fragrance. It has been around for decades and it never disappoints.
‘Burgundy Spice’. This Pleasant Run Nursery (N.J.) introduction has been an absolute standout in our trials at Yew Dell Botanical Gardens. Typical size, shape and flowers for the species but with deep and vivid burgundy coloration to the leaves that lasts through the whole growing season. One of our favorite summer shrubs! Read more about 'Burgundy Spice'.
Hybrids
:
‘Hartlage Wine’. This was the first, and it’s still a first-rate selection, if a tad on the large size. Richard Hartlage, then a graduate student working with J.C. Raulston at NC State University, crossed C. floridus with the newly introduced C. chinensis. The result was a vigorous and stunning selection. Easily growing 12 feet or more in height, it produces spring to early-summer crops of vivid red blooms with small yellow markings and very light fragrance.
‘Solar Flare’. Same parentage as ‘Hartlage Wine’, but it has a slightly more open growth habit and a bit more yellow on the inner tepals.
‘Venus’. This cross from Dr. Tom Ranney of NC State University includes blood of C. floridus, C. chinensis and C. occidentalis to outstanding impact. A compact grower becoming wider than it is tall, it produces huge crops of clear white blooms with a distinct banana-like fragrance. The blooms can be chewed a bit by insects but the overall impact remains quite good.
‘Aphrodite’. Tom Ranney’s best so far, this flowering machine is a cross of C. chinensis and C. occidentalis. Bright red flowers are carried at the tip and down along the stem over about two months in late spring and early summer. It is lightly fragrant; the scent of newly opening blooms is most noticeable, a mix of pineapple and even a little citrus.
Image credits:
Calycanthus floridus: Mad Ball/CC BY-SA 2.0
Calycanthus occidentalis: chuck b./CC BY 2.0
