Author: Ing. Uljana Blažková
Semi Evergreen Azaleas
These rhododendrons, known commonly as azaleas, can be evergreen or they can be deciduous. They belong botanically into Floccaceae group of rhododendrons. Semi evergreen species (subgenus Tsutsutsi) keep foliage over winter and they change it in spring. They include outdoor species and cultivars, but also indoor azaleas. Plant size is smaller as well as foliage. Deciduous rhododendrons (subgenus Pentanthera) loose their leaves in autumn and they flower mostly before new foliage sprout. These plants are bigger shrubs with larger leaves.
Semi evergreen rhododendrons are in collections in two display beds – one represents botanical species and second cultivars. Botanicals are e.g. Rhododendron macrosepalum – a Japanese species, which isn’t very hardy in local climate, foliage deciduous and flowers violet. R. obtusum is winter hardy, it is an ancestor of many cultivars and it comes from Japan. R. kiusianum is from South and Central Japan and it is a pioneer plant on volcanic eruptive rocks. R. kaempferi comes from the same area and it is also original species to many cultivars. Garden cultivars from this group are abundant, very attractive for bright flower colors and decorative autumn foliage. Botanically they are divided into several groups:
Hybrids from Rhododendron kaempferi
First of the cultivars developed in twenties of last century in Holland from hybridization of R. kaempferi s cv. Malvatica. These plants have quite large flowers mostly in pink shades. In this climate they are hardy. Cultivars ´Betty´, ´Fedora´, ´Orange Beauty´ can be found in the collection.
They come from R. mucronatum. It is a rhododendron with white flowers which is grown in gardens in Japan and China over 300 years. In 1910 a German breeder Georg Arends hybridized R. mucronatum ´Noordtianum´ with cultivars from Kurume group and he got ´Benigiri´, ´Hatsugiri´ and ´Hinodegiri´ cultivars. These plants had bigger flowers than Kurume group which you can compare in the collection: ´Agger´, ´Diemel´, ´Lister´, ´Uelfe´ and ´ Ennepe ´.
This is a group with long history in culture. It originates from Kurume Azalea (R. obtusum) and R. kiusianum. Both of these species have naturally a big variability, so some of cultivars are probably selected natural clones. In 1681 there were 147 cultivars grown in Japan and in 1720 it was 332. At the end of 17th century Ito Ihei wrote an illustrated book with 450 different forms of Kurume Azalea. Its common name comes from Kurume garden center near Nagasaki from 18th century. First cultivars brought to Europe by E. Fortun were from here. Plants from this group are of smaller size and with tiny but very attractive colorful flowers. There are several in the collection e.g.: ´Adonis´, ´Helena´, ´Kermesina´, ´Aladdin´, ´Amoena´
They originate from Dutch Booskop, where A. Vuyk in 1921 hybridized ´J.C. Van Toll´ cultivar (Mollis hybr.) with ´Mucronata´(R. mucronatum - hybr.) and ´Rose´ or ´Maxwelli´ (both Kurume hybr.). Later R. kaempferi was also used in this group. First nine cultivars had names after famous music composers like ´Schubert´ in our collection.
Deciduous azaleas have also two display beds in the collections and two of them complement semi evergreen species. One of them Rhododendron schlippenbachii have been grown from seeds collected in situ in Korea where it grows naturally. It can be also found in East Siberia, North-East China and Japan. It is a hardy azalea with big pale pink flowers, which can be damaged by frost, because it blooms in early spring. Second one is a very interesting species R. semibarbatum, which is the only one from subgenus Mumeazalea, while all other deciduous azaleas in the collection are of Pentanthera subgenus. It is a discreet small shrub with tiny leaves and very small milky-white flowers coming from Japan.
Other species of azaleas are together. Here you can find the only European deciduous rhododendron R. luteum with very fragrant yellow flowers. From American species, there are white flowering Western Azalea (R. occidentale) and Rhodora (R. canadense) which is very hardy plant with flowers in violet or white color. Asian species in the collection are represented by one of the famous rhododendrons - Japanese Azalea (R. glabrius) known commonly under its old scientific name R. japonicum or just Azalea mollis. This very attractive species was the original one for many cultivars of azaleas. Other interesting Asian species is R. albrechtii, very hardy Japanese azalea having bright deep pink flowers.
Cultivars of Deciduous Azaleas
They are very often, very attractive and they have advantage of tolerating sun. Of course direct sunlight causes short life of flowers. Botanically they are divided into these groups:
Knap Hill Hybrids
First cultivars of this group came from Knap Hill Nurseries, England around 1870 thanks to A.Waterer. Their origins were probably American species like white flowering R. arborescens, R. calendulaceum with orange flowers and R. occidentale together with Asian species like yellow and orange blooming R. molle. Today a lot of very attractive cultivars with bright colors are grown. In our collection they are represented by ´Balzac´, ´Berryrose´, ´Exbury White´ and others.
Name of this group is a horticulture term coming from an old name of Japanese Azalea (Azalea mollis, today R. glabrius). These cultivars have also ancestors in R. x kosterianum, which is a hybrid from selected lineage of R.molle. The beginning of this breeding was dated back to seventies of the 19th century and it was happening simultaneously in England (Mr.Tillery and Waterer), Belgium (Goennegen) and Holland (Koster). These cultivars belong, as well as previous group, to very attractive plants thanks to bright colors and hardiness. In the collection is e.g. ´Saturnus´.
Translation: Marketa Machackova