Trials of Rhododendrons at Wisley
Trials of rhododendrons conducted by the Rhododendron Association were started in the early 1930's at Exbury which was the estate owned at that time by the late Mr. Lionel de Rothschild. In 1938 the trials were moved to Wisley where most of the plants are now accommodated on 1¼ acres of land sloping to the north known as Battleston Hill, The trials are divided into three sections: 1) hardy hybrid rhododendrons, 2) evergreen azaleas and 3) deciduous azaleas. One plant of each entry is grown. All entries of hardy hybrid rhododendrons and evergreen azaleas are cultivated under woodland conditions being inter-planted amongst Oak, Birch, Sorbus, Pine and Magnolia.
Included in the hardy hybrid rhododendrons are large specimens of 'Mount Everest', 'Mrs. Furnival', 'James Burchett', 'Susan' and 'Langworth'. As an example 'Mount Everest', which received a First Class Certificate in 1958, has now reached 12 feet high and 14 feet across. The hardy hybrid section also includes small compact cultivars, e. g,. the plants raised by Herr Hobbie in Germany, and a fairly large plot which is devoted to R. yakushimanum crosses. The trial of hardy hybrid rhododendrons numbers 240 entries in 1974.
Cultivars in the evergreen azalea section include stocks of 'Betty', 'Satsuki' and 'Zampa' all of which have grown to approximately 5 feet high and 7 feet across. Entries from America, Australia and Holland are planted and the total number of plants for the 1974 trial is 114.
Deciduous azaleas are grown in the Portsmouth Field a recently developed part of the garden and number 118 different entries. Any selected garden form of azalea or hardy azalea hybrid is eligible for trial. This section includes a series of deciduous azaleas named after rivers in the United Kingdom which were bred at Wisley. The original breeding material was derived from Exbury Azaleas and these cultivars are accordingly included in the Knap Hill Hybrids group. As propagation material of the Wisley deciduous azaleas which have received awards is multiplied, material is released to the nursery trade for general distribution.
Plants in each section are individually labeled indicating the cultivar name, details or parentage when known, and the names of the originator (raiser) and the supplier of the plant to the trial. Entries which have received awards are labeled to denote the appropriate award and the year in which that award was made.
Most of the plants in the trial are supplied direct to Wisley from recognized breeders and nurserymen, although some are selected for trial by the Rhododendron and Camellia Committee at their meetings in London. In some cases entries are grown for purposes of comparison to help resolve problems of nomenclature and identification.
A sub-committee nominated by the Rhododendron and Camellia Committee usually visits Wisley at least three times during the season to report upon the trials and recommend awards. The sub-committee consists mainly of nurserymen and expert private gardeners who specialize in rhododendrons. Assessment of each plant is visual. During judging the sub-committee considers such factors as resistance to weather, health and vigor, improved flower form or color and floriferousness. At the time of inspection frequent reference is made to the flowering record of the plant. Details of flowering have been kept since the early 1950's and these indicate not only the date of flowering but also the amount of flowers produced each season i.e. below average, average and above average.
Awards made to rhododendrons after trial are as cultivars for general garden use. If an award for a plant is proposed and seconded voting takes place by a show of hands. The votes required for a First Class Certificate is at least three times the number in favor as cast against; for a plant to receive an Award of Merit or be Highly Commended the number of votes cast in favor is at least double the number cast against. All recommendations for awards are subject to confirmation by the Council of the The Royal Horticultural Society.
Horticultural descriptions are compiled for plants given awards and these include details of size of plant, foliage, size and shape of true, flower number and flower color which is matched with the R. H. S. Color Chart.
After the recommendations for Awards have been confirmed by the Council of The Royal Horticultural Society a list of the current seasons awards is circulated to all suppliers of plants to the trials. A detailed report including descriptions is subsequently published in Extracts from the Proceedings of the Royal Horticultural Society which is available to Fellows on application to the Secretary of the R. H. S.
Plants in the trial remain the property of the supplier and will, if so requested, be returned when the period of trial for a plant is terminated. In some cases the plants are offered by the supplier to the R. H. S. for planting elsewhere in the Wisley Garden. A cultivar is automatically deleted from the trials if it has not received any award after a ten year period at Wisley.
Wisley is also the center for the Plant Variety Rights trials for rhododendrons which are grown on behalf of the Controller of The Plant Breeders Rights Office which is U.K. Government controlled.
The R. H. S. endeavors to grow these plants intermingled with R. H. S. trial plants under average garden conditions. Rhododendrons in Plant Breeders Rights Trials can be recommended for R. H. S. awards provided the cultivar has been entered and officially accepted for trial at Wisley.