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Trial of climbing Lonicera (subgenus Lonicera) A recent trial at RHS Garden Wisley assessed climbing honeysuckles. Christopher Whitehouse summarizes the results 10 H oneysuckles are among our best known garden climbers. Valued for their beautiful scent and prolific flowers, they are an essential feature of many gardens. While flower colour can range from palest yellow to bright orange or deep red, the prized scent can be disappointing or even nonexistent if the wrong cultivar is chosen. Furthermore, cultivars with coloured leaves have recently become available, as well as hybrids of more unusual species. RHS / Barry Phillips Lonicera periclymenum Serotina Group ‘EM84’ The trial In 2006 the RHS began a trial of climbing honeysuckles with the aim of helping gardeners choose the best cultivars to grow. The trial focussed on species and hybrids of subgenus Lonicera – these are the ones with flowers in whorls at the end of the branches. Hence, the rather weedy, though strongly fragrant, Japanese honeysuckle, Lonicera japonica, and its relatives, were not included. They belong to subgenus Chamaecerasus, which also includes all the shrubby honeysuckles, and have their flowers in pairs in the leaf axils. Lonicera periclymenum The archetypal honeysuckle must be the UK native, L. periclymenum. It is common throughout the woods and hedgerows of northern Europe. Therefore, it is not surprising that numerous selections of this fine plant have been made. Two of the oldest, ‘Belgica’ and ‘Serotina’, date from the 17th century and are known as early Dutch March 2012 Plantsman The March 2012 Lonicera periclymenum Belgica Group ‘Belgica Select’ you a reliable garden plant. However, if you want to make sure of a high quality clone, then search for one labelled ‘EM84’. This clone was selected by the East Malling Research Station as the best from a selection programme they held for Serotina Group. A similar selection was conducted in 1977 by the Royal Boskoop Horti cultural Society in the Netherlands for Belgica Group, which resulted in ‘Belgica Select’, although the plant of this performed poorly in the trial. While the Dutch honeysuckles may be the oldest cultivars, more recent selections of L. periclymenum have been made. Several of these are named after where they originated, such as ‘Munster’, ‘Red Gables’ and ‘Chojnów’. However, they were not significantly distinct or better than the Serotina Group. But two selections did stand out. The first is ‘Graham Thomas’, probably the longest lasting and most floriferous of all the honeysuckles in the trial. It also seemed to have the strongest scent, although this might have been due to the sheer number of flowers. In contrast to the more popular selections of L. periclymenum, this cultivar does not have a red flush on the flowers but is a more consistent yellow and white. On the other hand, ‘Serpentine’ has superb dark foliage, which ➤ accompanied the dark red- RHS / Christopher Whitehouse RHS / Christopher Whitehouse Lonicera periclymenum ‘Graham Thomas’ RHS / Christopher Whitehouse honeysuckle and late Dutch honey suckle respectively. The distinction between these early cultivars in the literature was never clearly laid out. The primary difference appears to be based on flowering times, which nevertheless overlap. What is available today under these names is not consistent and almost certainly has changed considerably since the names were first used. It is recommended, therefore, that they be employed as Group names rather than cultivars. However, the Groups can still only be tentatively circumscribed as their definition is based partly on their relationship to each other in flowering time. Regardless of the naming difficulties, there is no doubt that there are fine garden plants available under these names, with striking bicoloured flowers of yellowish white flushed deep red, and a strong scent. Unfortunately, in the trial, the plants submitted as part of the Belgica Group performed poorly, which frustrated a good comparison with the Serotina Group. In contrast, the plants submitted as part of the Serotina Group were floriferous and strong. Although there was some variation among those submitted, buying one from the Serotina Group should give Lonicera periclymenum ‘Serpentine’ 11 Rhs trials flushed flowers and made a feature of the red berries. Unlike the variegated honeysuckles in the trial, the leaf colour did not appear to impede growth and it proved almost as vigorous as the Serotina Group. Lonicera x americana RHS / Barry Phillips Lonicera caprifolium ‘Inga’ RHS / Barry Phillips 12 Lonicera x italica RHS / Katy Prentice Lonicera x italica The next commonest honeysuckle found in gardens is Italian honey suckle, L. x italica, a hybrid between L. caprifolium and L. etrusca. It can look superficially similar to Serotina or Belgica Group, and has sometimes been mis-sold under those names, but unlike those L. periclymenum cultivars, L. x italica gives a one-off spectacle. Flowering in spring before L. periclymenum, it produces no further flowers, whereas most L. periclymenum will continue to produce some flowers after their initial flush. Botanically, the two can easily be told apart, as the leaves at the base of the flowerheads of L. x italica are fused together, whereas in L. periclymenum they are separate. There is debate over whether the common form of L. x italica found in gardens should be attributed to ‘Rubella’ or ‘Atropurpurea’. Rehder (1903) regarded both these names as forms, describing f. rubella as flushed purple and f. atropurpurea as flushed deep purple. The distinction is mild. As f. rubella is the earlier epithet, if someone wants to recognize the garden form with a purple flush to the flowers, it would be better to use the name L. x italica f. rubella. Despite the limited flowering season, L. x italica is reliable and has good scent. However, the variegated cultivar of this hybrid, L. x italica Harlequin (‘Sherlite’) is a weak plant and should be avoided. The name L. x americana has also been confused with L. x italica, but this misapplication was dealt with by Gorer & Harvey (1990). The former is later flowering than L. x italica, and Plantsman The continues to flower through the season. While L. x americana is botanically distinct, the plant in the trial did not perform well and showed no advantage over the hybrid that once usurped its name. RHS / Barry Phillips Lonicera caprifolium ‘Anna Fletcher’ Lonicera caprifolium and L. etrusca Lonicera caprifolium was the earliest to start flowering in the trial, beginn ing in April. It is fragrant and produces some of the showiest berries of the genus. Unfortunately, its early flowering means it starts to go over the soonest, the leaves beginning to brown by June. This can leave an unsightly mess for the rest of the summer, so its positioning should be considered carefully. Nevertheless, for the time it is looking showy, it is worth the effort of growing, especially if you choose one of the cultivars. The ones that stood out in trial were ‘Anna Fletcher’ (the plant grown in trial was entered as ‘Spring Bouquet’ but this is a synonym), and ‘Inga’, which was found in the wild in the Caucasus. Lonicera etrusca was best represented in the trial by the cultivar ‘Superba’. And this was a superb cultivar in every respect, being vigorous, floriferous, resistant to aphids, and well-scented. It is much later flowering than either L. caprifolium or L. x italica, peaking in June. The other cultivars of L. etrusca in trial, ‘Donald Waterer’, which has darker stems and redder flowers, and ‘Michael Rosse’, with lovely greyblue leaves, never established well and flowered poorly. Lonicera etrusca ‘Superba’ RHS / Christopher Whitehouse March 2012 Lonicera sempervirens and hybrids While the previous species are grown for the their scent and flowers, L. sempervirens lacks scent and is grown solely for its flowers. Its advantage is the much bolder flower colour, typically deep red with orange inside the tube. The flower shape is also distinctive, being narrowly tubular with only short lobes. However, the species does not do particularly well in the UK. The two cultivars in the trial, red ‘Cedar Lane’ and yellow ‘John Clayton’ both struggled. They are best-suited to connoisseurs who can give them the care they need. However, the species has been used as a parent in crosses designed to combine vigour with the colourful and distinctive flowers. The one that retains the most characteristics of L. sempervirens is L. x brownii ‘Dropmore Scarlet’. This hybrid with L. hirsuta has long, tubular, 2-lipped, red flowers with a few glandular hairs on the outside. In the trial it did not offer much improvement on its parent in terms of vigour. In contrast, L. x tellmanniana, a cross between L. sempervirens and L. tragophylla, was vigorous. Cultivars of this hybrid had the largest, most striking flowers in the whole trial. The best was ‘Mandarin’ with an abund ance of bright orange flowers. Strictly speaking, this is not L. x tellmanniana as its parents are L. tragophylla and L. x brownii, but it shows little evidence of the third species, L. hirsuta, in its parentage. Lonicera x heckrottii is a cross between L. x italica and L. sempervirens, but is much closer in appearance to L. x italica, only really gaining its ➤ bolder orange from the more 13 Rhs trials RHS / Christopher Whitehouse Lonicera sempervirens ‘John Clayton’ Lonicera x brownii ‘Dropmore Scarlet’ RHS / Christopher Whitehouse RHS / Christopher Whitehouse Lonicera sempervirens ‘Cedar Lane’ differences between species in the trial and their hybrids Leaves below Inflorescence inflorescence arrangement Leaf Flower persistence shape Flower hairiness (exterior) stalked, often in clusters of 3 inflorescences at end of shoot deciduous two-lipped short glandular hairs L.etrusca united stalked, often in clusters of 3 at end of shoot deciduous two-lipped glabrous* L. caprifolium united sessile, sometimes with deciduous two-lipped another whorl below long hairs interspersed with short glandular hairs* united L. x italica stalked or sessile, subtended deciduous two-lipped by much reduced united leaves; up to 3 inflorescences clustered at end of shoot long hairs interspersed with short glandular hairs as above glabrous** L. periclymenum free L. x americana united evergreen two-lipped united as above deciduous two-lipped L. x heckrotii L. sempervirens united stalked, sometimes with more than one whorl deciduous lobes +_ equal glabrous united stalked deciduous lobes equal L. x brownii L. x tellmanniana united very sparse short glandular hairs on young buds very sparse short glandular hairs on young buds stalked, sometimes in deciduous two-lipped glabrous clusters of 3 infloresences at end of shoot * in cultivated specimens in trial; some wild collections differ in hairiness. ** based on the single sample in trial. 14 March 2012 Plantsman RHS / Katy Prentice RHS The Lonicera x tellmanniana ‘Mandarin’ Lonicera ‘Spring Purple’ RHS RHS / Christopher Whitehouse Lonicera x heckrottii ‘Goldflame’ colourful parent. Unfortunately, it seems to have inherited reduced vigour from L. sempervirens and the plants in the trial were badly affected by pests and die-back in some years. However, it performed well in other years and the best was ‘Goldflame’ which has larger flowers and more deep yellow than the typical cross. Cultivars derived from Lonicera prolifera Two cultivars in the trial had L. prolifera in their parentage. These would best be classed as foliage plants, having limited floral beauty, but with intriguing cup-like bracts surrounding the flowers. They were at their best when fruiting, as the AGMs awarded to climbing lonicera subgenus lonicera Lonicera caprifolium * Lonicera etrusca ‘Donald Waterer’ * Lonicera etrusca ‘Superba’ • Lonicera x heckrottii ‘Goldflame’ # Lonicera x italica f. rubella # (AGM previously assigned to L. x italica) Lonicera ‘Mandarin’ # Lonicera periclymenum ‘Graham Thomas’ • March 2012 Lonicera periclymenum Serotina Group • Lonicera x tellmanniana # AGM recommended for removal for poor performance: L. tragophylla * AGM 1993 • AGM 1993, reconfirmed 2011 # AGM 2011 Lonicera ‘Fire Cracker’ glaucous bracts set off the orange fruit well, and they could make unusual components for flower arranging. Both were raised by plant breeder Peter Moore. Lonicera ‘Spring Purple’ has purple-tinged spring foliage and creamy flowers while L. ‘Fire Cracker’ has red flowers and more striking berries. Conclusion Overall, the trial emphasised that some reliable old plants, such as L. periclymenum Serotina Group and L. x italica, are still among the best when it comes to choosing a honeysuckle. However, there are some new innovations such as L. ‘Mandarin’ and L. periclymenum ‘Serpentine’ that are worth keeping a look out for if you want something that bit different to climb over an unsightly part of your garden. Christopher Whitehouse is Principal Scientist of the botany team at RHS Garden Wisley and runs the RHS Herbarium references Gorer, R & Harvey, JH (1990) The disappearance of Lonicera x amer icana. The Plantsman 12(2): 100–105 Rehder, A (1903) Synopsis of the Genus Lonicera. Missouri Botanical Garden, St Louis 15