The Rhododendron Trail

Here we preserve cultural heritage. Cultivars go out of fashion and are often forgotten, but some are tough enough to survive in old garden estates, from which we have taken cuttings. Good examples are the original pure white 'Cunningham's White', which was sold by Gerhard Stolz in Sandviken, for the first time in Norway around 1880, and which we have obtained from both his grandson Knut Fægri's garden and Mrs von Erpecom's garden. The same applies to 'Multimaculatum' (from 1850), which was found in a forgotten garden in Sunnmøre, laid out by a salmon lord about 100 years ago. It has almost disappeared even in its native England, where it was once very popular.

There is also a good representation of old English cultivars, and we even have the old French, deep violet 'Marcel Ménard', which has actually recently become popular again because of its dark violet flowers and hardiness. Some of the old German cultivars, which have gradually been outcompeted by more elegant, modern cultivars, stand out for their hardiness and abundant flowering.

We also show: 'Alfred', 'Chionoides', 'Christmas Cheer', 'Cunningham's Blush', 'Cynthia', 'Daphnoides', 'Effner', 'Gomer Waterer', 'Helene Schiffner', 'Herkules', 'Lady Anette de Trafford', 'Marcel Ménard', 'Moser's Maroon', 'Nobleanum', 'Nobleanum White', 'Pink Pearl', 'Purple Splendour', 'Sir Thomas Sebright', R. praevernum and R. ponticum 'Variegatum'.

Surprisingly few Rhododendron cultivars have been developed in the Nordic countries. The great diversity of international cultivars has been sufficient.

Finland, with its cold climate, has had it worst. They have begun developing their own cultivars, based on the very hardy R. brachycarpum ssp. tigerstedtii. These are not well suited to our climate, but several do well, e.g. 'P.M.A. Tigerstedt' and 'Pohjola's Daughter'. Breeding work has also taken place in Denmark, somewhat influenced by northern Germany. One of the oldest R. repens cultivars is named 'Aksel Olsen' after a well-known Danish breeder. There are also some newer Danish cultivars, of which we have, among others: 'Great Dane' and 'What a Dane'.

The Swedes have not distinguished themselves yet. There is a lot of activity, but some testing remains to be done. Norway does not have much to boast about either, apart from a few named 'bumblebee hybrids': 'Madam Felle', 'Hilario Lund', 'Vigdis' and 'Fritz C. Rieber'. In Eastern Norway, professor Harald Skjervold worked on rhododendron breeding; we show a selection of his best cultivars (unnamed). 'Our' most beautiful cultivar, however, is the excellent 'Arnulf', Arnulf Ringstad's cross of R. aureum and R. caucasicum.

We also show: 'Adalmina', 'Aksel Olsen', 'Axel Tigerstedt', 'Bergensiana', 'Eino', 'Elviira', 'Flava' × aureum, 'Fritz C. Rieber', 'Gedser Gold', R. tomentosum 'Golden Malin', 'Great Dane', 'Gudrun', 'Haaga', 'Helle', 'Hellikki', 'Helsinki University', 'Hilario Lund', 'Idun', 'Illusia', 'Inger', 'Ingrid', 'Jens Jörgen Sörensen', 'Jærperlå', 'Kaino', 'Kari's Surprise', 'Kullervo', 'Madam Felle', 'Marit', 'Marketta', 'Mauritz', 'Nenne', 'Nora', 'Northern Giant', 'Oldervik's Sigrun', 'Oldervik's Marion', 'Onnimanni', 'P.M.A. Tigerstedt', 'Pekka', 'Pohjola's Daughter', 'Raisa', 'Sissel', 'Skogbakken', 'Solveig', 'St. Michel', 'Tarleena', 'Tiuku', 'Tonje', 'Torill', 'Vason', 'Vieno', 'Vigdis', 'Vilde', 'What a Dane'.

The first hybrids were created based on a few hardy species with flower colours ranging from pale pink to violet.

Rhododendron breeding began in Britain towards the end of the 18th century, like so much else in gardening. The starting point was three closely related species: the American Rhododendron catawbiense and R. maximum, and the European R. ponticum. These gave rise to several hardy, somewhat 'stiff' cultivars that resembled each other and had flower colours from pale pink to violet. The oldest one we have is 'Roseum Elegans'.

Variation was limited, although forms with double flowers appeared, such as 'Fastuosum Flore Pleno', or with distinctive foliage, as in 'Daphnoides' and 'Variegatum'. It was only when the stately red-flowered R. arboreum was introduced from the Himalayas that a wider range of flower shapes and colours, and denser, rounder flower trusses, became available. 'Lee's Dark Purple' is the result of such an improvement. Other examples are the old pink cultivars 'Jacksonii' and 'Nobleanum' from around 1840.

We also show: Rhododendron catawbiense 'Album', R. catawbiense 'Grandiflorum', R. ponticum 'Roseum', 'Catawbiense Boursault', 'Cunningham's White', 'Cunningham's Dwarf White', 'Madame Carvalho', 'Nobleanum Venustum', 'Purple Splendour', 'Rosamundi'.

– And the story continues across the path...

Here we show a further development of the breeding work, often using Rhododendron arboreum.

Rhododendron arboreum from the Himalayas gave new impetus to the breeding work. It is itself a highly variable species, both in flower colour (from white to blood red) and in leaf shape and hardiness. This is reflected in the cultivars it has given rise to. There are entirely white-flowered types, such as the low, German Seidel hybrid 'Helene Schiffner'. But some of them have red flowers – and it took a long time to get these to be purely red, without a blue tinge.

Large flowers were also sought after, and this was not easy to achieve before species in the Rhododendron decorum group became available.

Another species of great importance was the yellowish-white R. caucasicum, which produced lower, denser plants and 'spotted' flowers. The well-known 'Cunningham's White' is one of its offspring.

We also show: Rhododendron oreodoxa, R. oreodoxa var. fargesii, 'Frank Galsworthy', 'Gomer Waterer', 'Lady Anette de Trafford', 'Midnight Beauty', 'Midsummer'.

The blotch in the flowers of many rhododendrons functions as a landing strip, of benefit to both the insects and the plant.

A great many Rhododendron species have a blotch in the throat of the corolla tube, most often purple, more rarely yellow-green. It serves as a guide for insects seeking pollen or nectar. For garden owners and flower lovers, it is the finishing touch that gives the flower particular character.

It is especially prominent in species that have contributed to the development of garden cultivars with spotted flowers: Rhododendron caucasicum and R. maximum. The German 'Humbolt' descends from R. maximum – long a favourite, but it now has improved successors including 'Kokardia'. R. caucasicum has been the most important in breeding. Among its offspring, the 'spotted noblewomen' have played an important role, and especially beautiful is 'Mrs. Furnival', and her children grouped around her, such as 'Mrs. Furnival's Daughter', 'Hachmann's Diadem' and 'Hachmann's Charmant'.

We also show: 'Azurro', 'Bariton', 'Belle Heller', 'Blau Jungs', 'Blue Boy', 'Blue Peter', 'Cherry Cheesecake', 'Edeltraud', 'Edwin O. Weber', 'Extraordinaire', 'Hachmann's Picobello', 'Hyperion', 'Ice Music', 'Kabarett', 'Kokardia', 'Kordesa', 'Le Progres', 'Loch Faskally', 'Marley Hedges', 'Marsalla', 'Mercator', 'Metallica', 'Mrs. T.H. Lowinsky', 'Olin O. Dobbs', 'Peter Alan', 'Pfauenauge', 'Sapporo', 'Schneeauge', 'Trail Blazer', 'Winter Spice'.

Rhododendron yakushimanum cultivars are very popular and well suited to modern gardens. The foliage is beautiful and the flowers come in many different colours.

On the rainy, damp and weather-exposed island of Yakushima at the southernmost tip of Japan, a small, dense, almost cushion-shaped Rhododendron with large white-pink bell-shaped flowers and dense brownish foliage was discovered in the 1930s. It was named Rhododendron yakushimanum. It went on to revolutionize the Rhododendron range after the Second World War – and especially from the 1970s onwards – with a series of low, dense, floriferous plants suited to small modern gardens.

Among the first to appear were Waterer's cultivars, aptly named after the seven dwarfs. We have only a couple of them: 'Bashful' and the pure red 'Dopey'. Over time, all the colours known from the tall cultivars have been bred in; indeed, even yellow ones – 'Flava' and 'Percy Wiseman' – are known. But otherwise, pink dominates. Exceptionally bright red is 'Lampion', a cross with R. repens, and the unsurpassed 'Fantastica', which lives up to its name.

R. yakushimanum cultivars are easy to grow and are very well suited to our climate. Over the years, they become quite tall.

Here we have gathered cultivars with many different origins, without being arranged according to a particular system.

It is not always easy to arrange plants with as mixed an origin as Rhododendron cultivars. Because we already had an older planting in Nydalen that had to be accommodated, the solution ended up like Sæverud's 'Peer Gynt' music – just as varied and colourful.

At the top, we show the newest reds from Hachmann, considerably clearer red than the best from the old days found directly opposite, on the other side of the path. This is thanks to Rh. griersonianum, which provided the final solution for pure red flowers. Look at 'Vulcan' in the middle – its colour is hard to improve on.

We also have some more unusual specimens: the double-flowered white 'Queen Anne's', and 'Ann Lindsay', which has two-toned flowers, red outside and white inside.

At the top, towards the path, stands a more uniform group: the Rhododendron insigne cultivars. They represent an entirely new development that has produced dense plants with glossy, healthy foliage and a splendid display of pink flowers. 'Brigitte' is the finest so far.

With the red carpet of flowers that appears in early May, the season is truly under way in Nydalen.

Rhododendron repens is a gift of nature to those who want pure red flowers, a goal many rhododendron breeders have strived for. The German Dietrich Hobbie knew how to make use of this. In the 1950s, he bred a series of compact, hardy and free-flowering cultivars, such as the well-known 'Baden Baden' and 'Scarlet Wonder'. By and large, only these crosses with 'Essex Scarlet' are known here, because they are excellent garden plants.

But there are more gems and much greater variation to be explored. Look at the early-flowering, lighter red 'Satin', the late, dark red 'Buketta', or the fiery, creeping 'Carmen'.

A completely new development, which has taken place particularly in the USA, is crosses with Rhododendron williamsianum. This has produced an entirely new type of rhododendron, such as the American hit 'Better Half' and its pink cousin 'Kimbeth' (across the path).

Rhododendron williamsianum and its hybrids develop bronze-coloured new leaves that emerge towards the end of flowering. This is very decorative.

Rhododendron williamsianum is one of the most elegant Chinese species, a compact beauty with glossy, distinctive leaves, and early flowering with pale pink bells. Unfortunately, it is a little temperamental to grow, but many good cultivars have been bred from it.

'Rødhette' (Little Red Riding Hood) is rather atypically late-flowering, with red bells. Most of its siblings come early in May with pink flowers, and with shoots and leaves that are bronze-coloured when young. This is especially well developed in 'Gartnerdirektor Glocker'. The dense, round growth habit is particularly pronounced in 'Vater Böhlje', which is also unusually hardy, but unfortunately has rather pale flowers.

Rhododendron williamsianum cultivars require an open, well-lit position to develop well and flower abundantly. They cannot manage without snow protection in colder areas. The flower buds swell so early that they can easily be damaged by spring frost. However, they can easily be forced into flower indoors.

The yellow cultivars are gathered on the flat area at the bottom of Nydalen. The colour ranges from clear yellows to those with very pale, washed-out flowers.

Truly yellow Rhododendron cultivars have been rare, simply because there are few yellow-flowered species in the wild. The first to be discovered was R. campylocarpum. It has creamy yellow flowers and gave rise to pale-flowered types such as 'Harvest Moon'. It has since been improved by Hachmann, who has bred, among others, the outstanding sisters 'Simona' and 'Maharani'.

Truly yellow cultivars only appeared in the 1940s, after R. wardii was discovered. This species has been widely used in breeding, producing everything from vigorous, large-flowered types such as 'Crest' to low, strongly yellow forms such as 'Goldkrone'. New cultivars are constantly being marketed, with many exciting ones from the USA that we are trialling at Milde.

Most Rhododendron wardii hybrids flower early, from mid-May. They suit conditions in Western Norway well, because they have a particular need for moisture.

In this area, we trial new introductions, and here you'll find many different cultivars grouped by which plants they were bred from.

Here you'll find surprises, unusual cultivars, and often some that have not yet been named. It is simply a trial field. But we have been reluctant to move the ones that thrive, so some cultivars that have since been named and become better known have stayed put. One clearly visible example is the yellow-flowered 'Golden Star', which has proven to be the most reliable of the new yellow cultivars from the USA. The large-flowered 'Golden Coach' has also been a pleasant surprise.

The still-unnamed Scottish R. macabeanum × wardii seems less promising. Hachmann's 'Herbstfreude' has splendid flowering from late May into June, although not in autumn as its name might suggest. 'Osterschnee' and 'Gulliver', two of his lesser-known cultivars, are both free-flowering and early. The latter is, surprisingly, a cross with R. adenogynum, a species with a reputation for producing offspring that flower poorly. It is also notable for its lovely, hairy foliage and dense growth.

This group consists of large plants that require plenty of space.

The dream of creating giant flowers was first realized when species of the Rhododendron decorum group became known, in particular R. griffithianum. They have not only given the flowers size, but also substance so they last longer, and in some cases also fragrance. The foliage is vigorous and handsome. The weakness is a tendency to develop a tree-like habit, with bare stems – as in the old classic 'Pink Pearl'. This last trait has been considerably improved in the American 'Scintillation', 'Lem's Monarch' and 'Trude Webster', perhaps the largest-flowered of all. Distinctly low-growing is the Czech 'Dagmar', which is also fragrant.

In this group too, a goal has been to achieve purely red-flowered cultivars. The noble old 'Jean Marie Montague' was outstanding in this respect, but it has now been surpassed by 'Grace Seabrook', 'Taurus' and 'Lem's Stormcloud'. It's hard to get a rhododendron darker red than the latter! But the best is probably the early-flowering 'Taurus'.

Some rhododendrons can, over time, become tall trees. They require a sheltered growing site to thrive.

This is a continuation of 'The giants'. Here we particularly want to show cultivars with parent species other than R. decorum, above all Hans Hachmann's with R. calophytum, a species otherwise little used; for example 'Caramba'. We also show his masterpiece 'Frühlingsbeginn', with the related, little-used R. sutchuenense as its mother. We also have one of the few crosses with R. niveum, the rare American 'Whidbey Island'.

Here you'll also find several of the finest and most delicate cultivars with mothers in the R. decorum group, of which 'Pink Pearl' and 'Loderi' are among the most famous. We show both these and some splendid hybrids that have them in their ancestry. 'Halfdan Lem' is the best red-flowered cross made by Lem, from Sogn, in his nursery in Seattle, USA. The plant was named in his memory – the most important Norwegian rhododendron breeder of all time.

There is much that distinguishes deciduous and evergreen rhododendrons, so it's not surprising that it is difficult to achieve crosses between them.

Crossing deciduous (azalea) and evergreen Rhododendron has always been an exciting challenge, as is often the case with anything difficult to achieve. Unfortunately, the result does not quite live up to the effort. A great many of the resulting plants have been short-lived and difficult to grow. They seem unable to decide whether to keep or shed their leaves in autumn. Even those that have survived look rather sorry for themselves and lack vigour, but the flowers are beautiful and unusual; the finest is 'Glory of Littleworth', which unfortunately is not so easy to grow.

Before Rhododendron wardii was available, yellow azaleas were the only ones that could give yellow flowers to the cultivars, and this is one reason they were crossed with, for example, Rhododendron ponticum. We have had great difficulty obtaining such Azaleodendrons and currently have only a couple of cultivars. They are not good garden plants, but they are botanically interesting.

The Mollis azaleas stand along the path and are recognized by their large flowers and strong fragrance.

These deciduous Rhododendron cultivars have mainly arisen through crosses of the two large-flowered species R. japonicum and R. molle. It was the Belgian Louis van Houtte who created the first ones as early as the 1870s. Later, the Dutch firm Koster in particular has developed new and better cultivars.

The colour range is somewhat limited, from yellow (rare), through flaming orange – e.g. 'Polly Claessens' or 'Christopher Wren' – to glowing red, such as 'Kosters Brilliant Red'. Something quite different is 'Appleblossom', which really is apple-blossom pink.

These are hardy plants that thrive best in full sun. They can appear somewhat stiff and stodgy, and their place has therefore largely been taken over by the more elegant Knap Hill types (see the bed above).

It was in Japan that rhododendron breeding began several hundred years ago. The plants were often clipped and used in temple gardens.

We know these best as potted houseplants, indoor azaleas. Botanically, they belong to the obtusum group, but are sometimes somewhat misleadingly called evergreen azaleas. Firstly, they don't always keep their leaves through winter; secondly, they are not very closely related to garden azaleas. They have played a significant role in Japanese, and later East Asian, garden culture – hence the name.

There are many types that have been given different names. The classic Kurume azaleas originate from the southernmost island of Japan, Kyushu, and are not very hardy here. One of the better ones is 'Hinomayo'. Of the famous hundred selected by Wilson, 'Geisha Orange' is the best.

Hardy cultivars have been produced particularly in the USA, for example the large-flowered Gable hybrids, in which Rhododendron poukhanense has been used. In Germany, the likewise very hardy but small-flowered R. kiusianum has contributed to the floriferous Diamant azaleas. It also features in the white, Scottish 'Panda' from Peter Cox.

Japanese azaleas are less commonly used in gardens in our part of the world; they require warmth and want to stand in full sun. They like good drainage and are not particularly peat-loving plants.

Knap Hill azaleas are good, hardy, floriferous plants that give the garden colour both during flowering in June and later when the leaves take on autumn colours.

Most of the so-called garden azaleas sold today belong to this group. It is named after the nursery in England where two generations of the Waterer family produced this new introduction at the end of the 19th century. They crossed the small-flowered Ghent azaleas with the large-flowered Mollis types. In this way, they achieved a wider range of both colour and form in the flowers, and managed to combine the best qualities of both groups.

The Knap Hill azaleas are constantly being improved and renewed, and it is easy to see how varied their origin is. The old rose-pink 'Homebush' closely resembles a Ghent azalea, while the new American large-flowered 'Mount St. Helens' looks almost like a Mollis azalea.

There are several 'lines' in the development, and some of these are given special names, such as the Exbury azaleas. These are all developed from the Knap Hill cultivar 'George Reynolds', and one of the first to be named was the glowing 'Hotspur Red'. Breeding work is also under way in Germany, and one of the best modern yellow cultivars, 'Goldpracht', comes from there.

The oldest garden azaleas arose from crosses of deciduous species from the American east coast.

These are the oldest, classic cultivars among deciduous Rhododendron. The pioneer of the breeding work was a Belgian baker, P. Mortier of Ghent. As early as the 1820s, he used the European Rhododendron luteum as a starting point and crossed it with two or three of the American species. The result was an entirely new type: the garden azalea – named after the city of Ghent, where they originated. Of the original cultivars, we have 'Coccinea Speciosa', the first 'flame azalea'.

In some, the stamens have transformed into petals, producing double flowers. These are often called Rustica azaleas. The best known is the old 'Narcissiflorum'. Also quite special is the large-flowered 'Nancy Waterer', an English cultivar from 1880. It was probably the first attempt to produce larger-flowered garden azaleas – which eventually became the well-known Knap Hill cultivars (see the bed above).

Despite their small flowers, the Ghent azaleas are valuable garden plants, and they can be forced into flower indoors in spring. They are undemanding, floriferous and often develop vivid autumn colours.

American azaleas have a strong fragrance, with flowers well into June, and they thus help extend the flowering season in the garden.

In the USA, there are 15 deciduous rhododendron species of the azalea type. Only one is from the west coast: Rhododendron occidentale. It is, however, the largest-flowered of all the American species, and also fragrant. It is also especially valuable because it flowers late. Crosses with Mollis azaleas have significantly extended the flowering season for garden azaleas. The best known is the old cultivar 'Irene Koster', but there is renewed interest in such crosses in the USA, and new introductions are constantly being launched.

Several of the other American species have also been used in breeding, for example in the Ghent azaleas (across the path). A quite special type has been developed from the strongly fragrant, small- and late-flowering Rhododendron viscosum. It has a distinctive, elegant effect, which is easily spoiled if it is placed together with the larger-flowered types. Most of the cultivars are in pastel shades, such as 'Soir de Paris'.

Evergreen plants with waxy flowers are not very hardy, but they have nevertheless done well in our collection.

In the easternmost Himalayas, there is a small group of Rhododendron with quite special, narrow, bell-shaped flowers, ranging from yellow to purplish red. This is the R. cinnabarinum group. The flowers are undoubtedly adapted for pollination by birds, as shown by their colour, shape and stiff, waxy texture.

Relatively few cultivars have been produced based on these species, but those that exist are special and elegant. Unfortunately, most are not very hardy here and need a sheltered spot. Several are also prone to mildew. The most reliable is 'Biskra'.

Rhododendrons with scales on the underside of the leaves are usually small shrubs, but here in the Triflora group the plants can become relatively large.

In this group, the flowers sit together in threes – hence the name: the Triflora group. They don't form large trusses, but cover the bushes so densely that the foliage is almost completely hidden. Strangely, they have never become particularly popular in our gardens, and they are little used in breeding.

They are shrubby relatives of the small, low alpine species found in '24. The blue slope', and have often been crossed with these to produce lower and denser plants, e.g. 'Russautinii' (= R. russatum × augustinii).

Truly lavish is 'Contina', with intensely saturated red-violet flowers. And we must not forget the Arboretum's own production, 'Madam Felle', which was christened by then-mayor Henrik Lisæth – in beer, naturally – at the opening of the Rhododendron Garden in central Bergen. It is a so-called 'bumblebee hybrid' of Rhododendron concinnum, one that came about through the random flight of a bumblebee.

The alpine roses are small plants suited to the rock bed, and they want plenty of sun.

The first Rhododendron to be described was a small, dense shrub from the Alps. This is why rhododendrons are often called 'alperoser' (alpine roses) in Norwegian. The true alpine roses, however, are quite different from 'ordinary' rhododendrons. They are low alpine plants with scaly leaves and small pinkish-red flowers.

The three species in this group, R. ferrugineum, R. hirsutum and R. myrtifolium, have not been much used in breeding, and the cultivars available commercially are relatively rarely planted in gardens.

We have also placed here the few known cultivars in the closely related Pogonanthum group. Especially interesting is 'Arctic Tern', a cross with marsh Labrador tea (Rhododendron tomentosum), which was previously classified in the genus Ledum. More recent research has shown that marsh Labrador tea naturally belongs as a branch on the evolutionary tree of the Rhododendron genus, and is not a separate lineage within the heather family alongside it.

Across the path, we continue with cultivars of other species with scaly leaves (lepidote). In particular, the Rhododendron saluenense group has produced a number of fine, low-growing, large-flowered plants, such as 'Lavendula'.

These are small cultivars with yellow flowers. They form a fine contrast to the blue ones on the other side of the path.

Yellow is not a common flower colour in wild Rhododendron, nor among low, evergreen species. Until recently, this was reflected in the few cultivars available commercially. There was really only one: the very distinctive 'Yellow Hammer', which is also not very hardy here.

Fortunately, two breeders became interested in low yellow cultivars: Peter Cox in Scotland and Warren Berg in the USA. Berg has mostly used the Japanese Rhododendron keiskei as a starting point.

This has produced many fine, pale yellow cultivars, such as 'Patty Bee'. By crossing in species with pink colouring, he has also produced cultivars with striking shifts between yellow and pink: 'Ginny Gee' and 'Too Bee'.

Cox has used a wider range of parent species, including the large-flowered R. ludlowii, a species that is very difficult to grow. It is almost a miracle that he has produced so many outstanding garden plants with such unreliable parents. 'Curlew' is probably the finest of all the low yellow cultivars.

Short-growing rhododendrons with blue flowers are alpine plants and Asian relatives of the Norwegian Lapland rosebay.

One of the few wild Rhododendron species in Norway is R. lapponicum. It has given its name to a large group of alpine species, found particularly in the Himalayas. They are dense, small-leaved, cushion-forming species with flower colours mostly in the violet range.

Selections of these became popular relatively early, particularly as rock garden plants. One of the oldest, and still popular, is 'Blue Tit' from the 1930s. Another classic is 'Blue Diamond'. Both contain R. augustinii, a species of the Triflorum group (see '21. The trinity') with beautiful, pale blue flowers, but poor foliage that easily looks sickly. Breeding work has focused on eliminating this, while also achieving hardy plants with flowers that do not fade in sunshine.

Many good new cultivars have come particularly from Germany and the USA. Among the hardiest are: 'Gristede', 'Mother Greer' and 'Ramapo'.

The flower colour also varies from very dark blue-violet, as in 'Azurika' and 'Night Sky', to light sky blue in 'Blaumeise', 'Blaubart' and 'Frost Hexe'.

These are rhododendrons that can flower in the middle of winter, provided there is mild weather over an extended period.

Two unusually hardy species come from East Asia: Rhododendron dauricum and R. mucronulatum. They are the basis for a number of early-flowering cultivars that can withstand the most extreme cold and draughts. The climate in Bergen is actually too mild, so they don't always develop as well as they might. The plants have only a brief winter dormancy, and such low temperature requirements for growth that they often flower during mild spells in midwinter here. In subsequent frosty periods, it doesn't take many degrees of frost to set them back. The most widely used from this group is the well-known 'Praecox', which originated as early as 1860.

Many better cultivars have come particularly from the USA, where work has been done to produce cultivars that can withstand the harsh climate of the north-east around the Great Lakes, for example 'Anna Baldsiefen'. By using another hardy species, R. minus, entirely new types have also been produced (see 23 The cold corner). 'February Dawn' is the earliest of all. These are also suitable for forcing indoors in winter.

Most rhododendrons thrive best in a mild winter climate, but some are hardy and can tolerate very low temperatures.

In attempts to produce cultivars that could be used in the coldest regions of the USA, Rhododendron dauricum was crossed with R. minus. This gave rise to some of the hardiest rhododendrons known at all. Even the flowers can tolerate a little frost, and the plants survive as far north as Alaska.

Offspring of this cross were introduced under the curious name 'P.J.M.'. These are the initials of the breeder P. J. Mezitt, and plants that were not entirely identical to one another were sent out from his nursery. A selection has since been made among them, and several have been named separately, for example 'Elite' – a particularly large-flowered variant.

 Similar crosses have also been made with different forms of the parent species, and there is now a whole range of cultivars that vary in flower colour from white through pink to violet. They all like an open, well-lit position and can tolerate cold, draughts and drought.

Some rhododendrons are not very hardy and are placed in a separate collection – the Treasure Chamber. The pine forest contributes to a sheltered and relatively sunny local climate.

Here we have hidden some of the least hardy cultivars, those that need particularly good growing conditions. The star among these gems is 'Lem's Cameo', which needs plenty of nutrients to flower abundantly.

There are also several low cultivars here, in which the not very hardy R. ciliatum and R. edgeworthii have been used with success to create low, decorative cultivars that are unfortunately sensitive in our climate. These are cultivars that require especially mild and well-protected growing sites. The only one that seems to be more widely usable is the early-flowering, white 'Sanderling', which is also found at '25. The draughty corner'.