Hardy chrysanthemums
Plantsman Jonny Bruce selects the best of the late-flowering, hardy chrysanthemums and offers expert tips on propagation
For the past three years I have been part of the small team at the organic plant nursery, De Hessenhof, in the Netherlands. Walking on to its stock beds in October and early November, I’m still struck by the beacons of yellow, pink, orange, white and red that glow among frost-blackened foliage and brown skeletons. These hardy chrysanthemums are one of the specialities of De Hessenhof, which was started almost 40 years ago by Hans Kramer and his wife Miranda. While hardy chrysanthemums have suffered from the persistent myth of being fussy and tender perennials, in the past 20 years or so, they have been re-established as a mainstay of the autumn garden.
Hardy chrysanthemums probably reached peak popularity in the UK before the Second World War, largely down to the work of master nurseryman, Amos Perry. At his Hardy Plant Farm in Middlesex, Perry developed many celebrated cultivars in the inter-war years, some of which are still in cultivation. In 1933 a plant with a compact habit and soft-pink flowers had appeared at the Royal Botanic Gardens, Kew. Tentatively named C. erubescens, it was later described in 1938 by Kew botanist Joseph Robert Sealy as
C. x rubellum (but this is now recognised as belonging to C. zawadskii). Perry got his green-fingered hands on this plant and immediately incorporated it into his breeding programme. The first introduction from this new bloodline was C. ‘Clara Curtis’, the first of what became known as the Rubellums. Considered one of the best plants for late summer, ‘Clara Curtis’ is reliably smothered with soft-pink blooms, each with a cheery yellow eye, from August until October, and still features in the catalogue at De Hessenhof.
In the early 20th century, improvements using forms of C. zawadskii were also taking place in the USA at the Bristol Nursery of Alexander Cummings in Connecticut. JG Jack of the Arnold Arboretum in Boston had introduced a plant from Korea under the name of C. coreanum (now recognised as
C. zawadskii subsp. coreanum). By 1928 Cummings was using seeds from this plant to develop his famous Koreans, which introduced American gardeners to a whole new range of colours and f lower shapes. Many nurseries still divide hardy chrysanthemums between Koreans and Rubellums but the reality is there has been so much breeding between the two groups that they have become indivisible. It is easier to divide hardy chrysanthemums between the compact, early forms that f lower from June to September and the later and taller cultivars that tend to last into November.
Unfortunately, in the 1940s, many old garden cultivars were lost, as ornamental plants made way for vegetables to help the war effort. The post-war years saw a revival of the show blooms, mostly variations of the tender and definitely fussy C. indicum, which fostered misconceptions about this diverse group of plants. The development of mass-produced all-yearround chrysanthemums, synonymous with forlorn petrol station forecourts offerings, has done little to promote the garden-worthiness of the genus.
Modern breeding techniques tend to focus on compactness and bright colours over longevity and many new cultivars struggle to live up to the gardenworthiness of their older counterparts, but that is beginning to change. No gardener has done more to restore the popularity of hardy chrysanthemums as National Collection holder, Judy Barker. It was Judy who, in collaboration with the late chrysanthemum expert, Barrie Machin, helped co-ordinate – and provide plants for – the RHS trial at Wisley in 20102012. Despite harsh weather during the trial – December 2010 saw temperatures plunge to -17°C, while March 2011 was the hottest since 1659 – most of the 130 entries flowered well with 20 cultivars being awarded an Award of Garden Merit.
Hardy chrysanthemums in the collection at De Hessenhof have proved themselves over many years and, although the RHS has given most a hardiness rating of H4, meaning they are hardy to temperatures of around -5°C to -10°C, the average for a UK winter, many have survived Dutch winters down to -20°C. The colours range from whites and soft pinks to rusty orange and fiery reds, and all look good when set against a palette of autumnal browns. Some cultivars will benefit from having their buds pinched out in early June, the result being more branching and less staking.
Most are well suited to a sunny border and are adaptable to a range of soils – although they prefer not to sit wet during the winter and resent drying out in the summer. A good feed of organic fertiliser in spring and a mulch layer to retain moisture will set them up for the rest of the year. The pleasing mass of silvery foliage is an excellent foil for other plants earlier in the year and as the frosts begin to nip there are few flowers for which a gardener can feel so grateful.