This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Although cultivated by the Dutch as long ago as 1680, this species, which covers every hill and mountain in Central and Southern China, was only taken seriously in hand by nurserymen about eighty years ago. Since that time innumerable varieties, double and single flowered, have been evolved, and hundreds of thousands of plants are now raised annually in the Dutch, French, and Belgian nurseries for export to Britain, America, and other parts of the world. It is curious that while in British nurseries the custom is to pot the plants very hard in a peaty compost, the reverse is the case in Continental nurseries, where the plants are grown magnificently in a loose peaty mould in frames, and in the open air during the summer months. The named varieties are usually grafted on common stocks, which are themselves raised from seeds or cuttings. Nice bushy plants, suitable for 3-in., 5-in., and 6-in. pots, are now readily obtainable for winter blooming, and a good trade is done in them just before Christmas and afterwards well into March and April. The blooms are very beautiful, and vary in colour from the purest white to the deepest scarlet and crimson through shades of purple, many varieties being gorgeously striped or spotted with other quite distinct shades. Amongst the most popular coloured varieties the following may be mentioned: Apollo, bright red, semi-double; Marc Rouman d'Ertbuer, deep crimson, double; Flambeau, magenta red; Ferdinand Kegeljan, deep rose, upper petal speckled; Mar-quis of Lome, bright fiery red; Comtesse de Flandres, magenta rose, very large; Anna Klein, double white, sometimes splashed and spotted with red; Alexander II, blush, speckled crimson; Prof. Walters, blush white, upper petal speckled deep rose; Oberst von Kutsinsky, scarlet, double; Spitfire, brilliant crimson scarlet, double; Theodore Riemers, clear magenta purple, double; Vervoeneana, double white, rose centre, upper petal heavily blotched with crimson; Eclair, deep brilliant crimson; Lady Roosevelt, clear flesh pink, semi-double; Rudolf Seidel, deep flesh pink, splashed with crimson.
Fig. 262. - Double Azalea (Deutsche Perle).
For cut flowers some growers still grow large specimen plants of the old "Fielder's White" Azalea - a beautifully pure-white single-flowered form. Quite large plants, from 3-8 ft. high, are grown in pots or tubs, and are forced into early bloom for Christmas and onwards. The flowers are bunched up in dozens, two or three on a stalk cut as long as possible, each individual bloom being gummed beforehand. After standing in water for an hour or two, the flowers are carefully packed in shallow boxes and protected with tissue paper. Sometimes they realize good prices, from 3s. to 6s. per dozen bunches, but at other times they are a drug in the market. For wreath work and funeral emblems generally, this pure-white Azalea is difficult to beat. Other good white varieties are alba, alba magna, and magnifique.
Amongst the double whites useful for the cut-flower trade are Deutsche Perle (fig. 262), Borsig, narcissiflora, Flag of Truce, Madeleine, Heine de Portugal, Bernard Andrea alba, Eros, Niobe, Sakountala, etc. (See also fig. 263).
After Azaleas have finished flowering they should be pruned and thinned out, and then grown on in a warm greenhouse temperature and well syringed in the morning and afternoon, in addition to giving fair supplies of water to the sandy and peaty compost in which they should be grown and firmly potted. In this way long clean shoots are made early in the year, and by the end of May or by the middle of June the plants may be stood out in the open air till about September or until there is a danger of frost. During the summer months the plants must be watered thoroughly when necessary, and each day should also be well syringed early in the morning and late in the afternoon to encourage and ripen the growth, and to prevent attacks of Red Spider and thrips - pests that are likely to be very troublesome in hot dry seasons.
Fig. 263. - Azalea indica, single.
Under glass the plants, if afflicted, should be fumigated or vaporized two or three evenings in succession to free them from pests or to prevent attack. Old plants may be grown in the same soil for many years in succession, and if supplied with weak liquid manure water when the buds are swelling they will yield enormous crops of bloom.
Azaleas flourish in sandy loam or peat, but the latter is generally preferred. M. Georges Truffaut, who has paid special attention to the chemical composition of the Indian Azalea and the soil in which it grows best in parts of France and Belgium, gives the following figures for four kinds of Continental leaf mould: -
Leaf-mould from Rambouillet.
Leaf-mould from Maurepas.
Peat-mould from Maurepas.
Quantity of Fine Mould in 1000 lb. bulk,
Nitrogen ... ... ...
Phosphoric acid ... ...
Lime ... ... ... ...
Potash ... ... ... ...
Silica ... ... ... ...
Iron oxide ... ... ... ...
Organic matter ... ... ...
It will be noticed that the Ghent leaf mould, which is famous for Azalea culture, is more abundant in nitrogen, lime, and organic matter than the other samples, and this may give a clue to mixing up a suitable compost. Analysis of the ash of the different parts of an Azalea give the following figures: -
Leaves ... ...
Stems ... ...
Roots ... ...
From these it may be inferred that the practice of adding sharp sand to Azalea compost is justified by the amount of silica taken up by all parts of the plant.
INDIAN AZALEAS AND MYRTLES UNDER GLASS.
There is one point to remember about potting, that is, never to use pots larger than necessary. Quite large-headed plants full of bloom may be grown well in 3-in., 5-in., and 6-in. pots, and for market work it is a consideration not to have too great a weight to carry.