Lulstraat 3, 9770 Kruishoutem
Azalea japonica or EVERGREEN GARDEN AZALEAS
The main varieties from which today's garden azaleas are derived are:
Rh. kaempferi, this is found all over Japan and grows mainly in the shade of trees on the side of hills; it has an ascending growth. The shrubs reach a height of between 1 and 3 m. Its flowers are red.
Rh. kiusianum is found mainly on the island of Kyushu. This pioneering plant grows on volcanic subsoil. It is very resistant to air pollution caused by sulphur dioxide. They are frequently beaten back by new volcanic eruptions, but they always re-colonise the volcanoes. Once a volcano is extinct, R. kiusianum also covers the inside of the volcano, hence its Japanese name miyama which means “the inside of the mountain”. The maximum height of this spherical plant is 1 m. The flower colour ranges from purple to lilac, with red and white being rather rare.
R. kiusianum can overcome large differences in temperature and withstand direct sunlight, but requires a lot of water and a subsoil with very good draining properties (lava).
Rh. sataense Nakai is usually classified as a variety of R. kiusianum, but is only found in the Takakuma mountains. R. sataense grows in a more isolated fashion and its flowers are purple, carmine and red.
On the island of Kyushu a natural hybridisation took place between R. kaempferi and R. kiusianum, which was named R. obtusum planch by Ernest H. Wilson (associated with the Arnold Arboretum in Boston) and introduced to the United States in 1916. In 1920 almost the entire Wilson range was introduced to the Netherlands by C.B. van Nes; this was the basis for the dissemination of Japanese garden azaleas throughout the western world.
In order to derive many years of enjoyment from your azaleas, it is important to know how hardy these plants are. In our list, we have given an indication of how hardy each variety is, insofar as this information is available to us (for some varieties that are still relatively new to the Belgian market, we are currently testing them in the garden – please ask us for our findings when you purchase one of these plants.)
In severe winter conditions people sometimes believe that certain azaleas are frozen, when very often they are simply dehydrated; make sure that the planted azaleas are given sufficient water for the winter (but never water during periods of frost).
Above all, when planting azaleas, make sure that the subsoil is permeable.
If the subsoil is sandy, mix in plenty of peat or woodland soil in the top layer; this increases the volume of air in the soil and is also a good buffer for water and fertiliser. It is possible to keep azaleas alive even in soil with poor permeability, but in this case a raised bed should be used: make a border around 40 / 50 cm high, fill it completely with a mixture of pine leaf compost and peat, make sure that excess water can escape through slits in the side, press the soil down firmly when planting (if you are planting in peat, you do not have to press so hard).
The best time for planting azaleas and rhododendrons is from mid-October to mid-November and in spring from mid-March to the end of April.
Japanese azaleas can first be allowed to flower indoors and then planted outside, but this requires a lot of energy from the plant; water them copiously, especially in the first year, with around 10 l per m² per week (after that it is sufficient to water them only in dry periods).
Apart from that, azaleas require little in the way of care. Deadheading is good for the plant, as it enables the new shoots to develop better.
After flowering, the plant should be fertilised, preferably with a slow-acting fertiliser with an NPK ratio of 3 - 1 - 2; spread approximately 10 grams per plant (for a plant with a diameter of about 50 cm) around the root area, bearing in mind that the roots extend approximately as far as the outside of the plant.
Azaleas do not need to be pruned. If you nonetheless wish to cut back some branches, it is best to do so immediately after flowering.
Japanese azaleas colour our gardens with their magnificent flowers from the end of March to the end of June (R. nakaharai). But in the autumn they can also transform the garden into a veritable symphony of autumnal colours.