Within the family Calycanthaceae there are four diverse genera of shrubs, three of which offer the UK designer or gardener excellent options for the fragrant garden. The well-known wintersweet Chimonanthus is one, which bears its fragrant, waxy yellow flowers on bare stems in winter. Its cousin Calycanthus or sweetshrub also has fragrant flowers, though they are typically dark red and appear in the summer and early autumn.
Less well-known horticulturally is the third genus, Sinocalycanthus, originating from China. There is only one species in cultivation in the UK, S. chinensis, introduced by plantsman and author Roy Lancaster in 1989. From that genus a hybrid known as x Sinocalycalycanthus has been bred, after crossing with Calycanthus and a couple of interesting and sought-after cultivars are available in this country.
Chimonanthus praecox is a mainstay shrub for providing winter interest and fragrance through its waxy yellow flowers with purple centres. But within the genus there is also an evergreen species, C. nitens with white flowers and other attractive bi-coloured varieties. Plants will need protection from heavy frosts that may damage the blooms.
There are two species of Calycanthus cultivated in this country — C. floridus and C. occidentalis. Both are medium-sized deciduous shrubs with aromatic bark that bloom in the summer. Both have fragrant maroon-coloured, many-petalled flowers, but C. occidentalis is a larger shrub with larger leaves and purple-brown flowers. C. floridus has dark red-brown flowers and is the most frost-resistant.
They should be planted in deep, moist, humus-rich soil in a position where the shoots can ripen fully before the winter. Pruning should be restricted to the removal of deadwood. Propagation can be done by layering, division or removing suckers in the spring.
Sinocalycanthus chinensis was formerly known as Calycanthus chinensis but is now classified as a monotypic genus of its own. It is a deciduous shrub reaching to 3m in height with large glossy green leaves and creamy white magnolia-like flowers.
These should be planted in a warm spot in full sun or light, dappled shade. They prefer well-drained yet moist, fertile soil and do not grow well in shallow, chalky soil. Though hardy, they appreciate protection from cold winter winds. The large leaves can be a tempting target for slugs and therefore controls are advised.
WHAT THE SPECIALISTS SAY
Karan Junker, co-owner, PMA Plant Specialities, Somerset "With Chimonanthus it is important that people buy named cultivars, because it takes so long to flower from seed. It doesn't have the diversity of some genera, but it does have the nice winter scent to recommend it.
"The plain yellow-flowered varieties such as 'Luteus' are very nice, but personally I like the varieties with bicoloured flowers. My favourite is 'Sunburst', which is a selection we made here at our nursery. Its name was suggested to us by Roy Lancaster. It has large flowers in a good strong yellow. They have a red centre that lends them warmth.
"In terms of cultivation, Chimonanthus can be a bit tricky to establish, so don't plant them too small. They need a good sunny site, which helps ripen the wood and leads to a better scent, and they don't like it too wet in the winter.
"There is a gorgeous plant related to Calycanthus x Sinocalycalycanthus raulstonii 'Hartlage Wine', which I like. The variety has large maroon flowers, which have a light scent and glossy green leaves."
Steve Dance, office manager, Burncoose Nurseries, Cornwall "Calycanthus floridus has lovely deep carmine, magnolia-like flowers. It becomes a nice shaped shrub and is a reliable flowerer. It's viewed as a bit of an old-fashioned plant these days but surprisingly we still sell quite a few.
"There is also C. occidentalis, which grows up to 3m tall and provides good autumn colour. It has similar flowers to C. floridus. The plants will grow on most soils and are generally free of trouble from pests and diseases."
Tracey Armstrong, nursery assistant, Larch Cottage Nurseries, Cumbria "Chimonanthus praecox is the most popular variety, with its very fragrant yellow, purple-centred flowers. We also grow 'Nitens', which is slightly less fragrant but has attractive white flowers.
"One that is rarely available but worth looking out for is 'Brockhill Goldleaf' for its golden foliage. We sell a few Calycanthus as well, including C. floridus, which has attractive red flowers between July and October, and its cultivar 'Michael Lindsay'."
Amanda Patton, garden designer, Somerset "Chimonanthus should be planted quite close to the house because it needs the warmth — the flowers will become damaged if exposed to frost. Get it planted in the right spot and it will do really well and reward you with its fantastic fragrance.
"To my mind it provides the best of the winter scents. It may not be significantly interesting after flowering, but the smell is so spectacular it is worth using. It's also really nice as a cut flower. Display it with some snowdrops in a vase.
"It is a shrub for a big garden with plenty of space. It takes a few years to get going and its flowering is unreliable because it is prone to the weather conditions. If designing a winter garden I would use it alongside Sarcococca, Salix and Cornus, perhaps with clipped box underneath providing structure."
SPECIES AND CULTIVARS
Chimonanthus nitens is a rare evergreen species with shining oval lanced-like leaves. It bears large, solitary white flowers.
C. praecox is the main species in cultivation. It is a medium-sized, deciduous shrub with sweetly scented, pale yellow, waxy flowers, which are stained purple in the centre. They emerge on the shrub's leafless branches during the winter.
C. praecox 'Brockhill Goldleaf' is a gold-leaved variety that is rarely available.
C. praecox 'Grandiflorus' Award of Garden Merit (AGM) is a form with deeper yellow flowers, strongly stained with red.
C. praecox 'Luteus' AGM has large, unstained flowers that are a uniform clear waxy-yellow. They open later than those of the typical form.
C. praecox 'Sunburst' has strong yellow flowers with red centres, which are larger than the type.
C. praecox 'Trenython' is a rare cream-flowered form that originated in Cornwall.
C. yunnanensis is similar to C. praecox.
Calycanthus floridus is a large, rounded deciduous shrub with dark glossy green and aromatic leaves, which are downy beneath. It has many-petalled maroon flowers that smell like ripe apples during the summer. With a cold snap in autumn, the leaves turn yellow before falling. Height 2.5m and spread 3m.
C. floridus 'Athens' is a rarely-available form that features extremely fragrant, pale yellow flowers.
C. floridus 'Michael Lindsay' is an American clone that was selected for reliable and profuse flowering as well as larger and darker blooms. The flowers are maroon-chestnut and smell like cloves.
C. floridus var. glaucus has dark red fragrant flowers and smooth wood. Also known as C. fertilis and C. floridus var. laevigatus.
C. floridus var. glaucus 'Purpureus' is a rarely-available shrub. It features aromatic downy foliage and maroon flowers like the type, but the leaves are purple on the underside.
C. occidentalis has larger flowers and leaves than C. floridus. Height 3m and spread 4m, flowers purple-brown.
Sinocalycanthus chinensis is a deciduous shrub reaching up to 3m in height. It bears lovely large creamy-white magnolia-like flowers with yellow centres in mid-summer. The leaves are of variable size, but oval and glossy green. It was first introduced to Britain from central China in 1989 by Roy Lancaster.
x S. raulstonii 'Hartlage Wine' was introduced from the JC Raulston Arboretum in North Carolina. It is very rare in the UK and commands a high price. It has lightly scented maroon-coloured flowers that grow up to 7.5cm across.
x Sinocalycalycanthus 'Venus' is a descendant of the hybrid x Sinocalycalycanthus raulstonii 'Hartlage Wine', which was then crossed with a Calycanthus species. It has beautiful magnolia-like white flowers with an alluring fragrance.