Gladiolus. (Gladiolus species and hybrids; Family Iridaceae). With its majestic flower spikes with massive florets of brilliant colours, attractive shapes, varying sizes and excellent keeping quality, the gladiolus is ideal both for garden and for cut-flowers. It was brought into cultivation from its native habitat in South Africa, perhaps during the ancient Greek period. Its systematic improvement began only in the early years of the present century after the discovery of the Primulinus (Gladiolus primulinus), gladiolus growing wild near the Victoria Falls in South Africa. The hybridization of Primulinus and a few other species, e.g. G. byzantinus, G. psittacinus, G. cardinalis, G. childsii, G. colvillii and G. gandavensis, resulted in the present-day gladiolus. It is undoubtedly the best bulbous flower in our country and ranks next only to tulips in Holland and other countries.
USES. Gladiolus is excellent for growing in beds and pots and as herbaceous borders and for cut-flowers. As soon as the first floret has started opening and the others are showing colour, the flower spike is cut neatly with a sharp knife and is immediately placed in water. The other top florets will then open gradually and last for a long period.
TYPES AND VARIETIES. The two most important types are the large-flowered varieties and the butterfly or the miniature gladioli. Both types are early, mid-season and late-flowering requiring 65-75 days to 100-120 days for flowering. The butterfly types have small spikes of various colours and in many cases with dark and attractively coloured throats. They are ideally suited for small gardens and flower arrangements. Besides, the primulinus and colvillei are two other types; the former have small florets borne on thinner spikes with a hooded top petal in each floret. Psittacinus hybrids are also popular in gardens.
The flowers of gladiolus may be large, medium or small, sometimes with petals ruffled, blotched or streaked. The colours range from white to near black, including pink, salmon, orange, red scarlet, maroon, yellow, greenish, purple, lilac, mauve, violet and several other shades. Some varieties are also dark or 'smoky'. There are also double-flowered varieties. Recently, scented gladiolus varieties have been evolved through the hybridization of Gladiolus with Acidenthera bicolor var. murielae. This intergenic hybrid is known as 'Gladenthera' and one such variety is 'Lucky Star'.
The important varieties are : 'George Mazure', 'Fay', 'Gold Dust', 'Tunia's Yellow Triumph', 'Elizabeth the Queen', 'Jo Wagenear', 'Spic and Span', 'Spotlight', 'Dream Girl', 'Goeff Whiteman', 'Blaur Dominos', 'Polygoon', 'Banaras', 'Mary House', 'Snow Princess', 'Ratnas', 'Butterfly', 'Masholra Butterfly', 'Sylvia', 'Apple Blossom' and many others.
CULTIVATION. Gladiolus grows almost equally well in beds and pots. The beds should be dug out thoroughly and prepared finely. Before the final preparation, rotted cowdung manure, leaf-mould or compost about 5 to 6 kg and superphosphate 60 g per square metre may be added to the soil.
Gladiolus is generally planted from corms. It can also be grown from seeds, but the variety does not breed true in such cases. Propagation from seed is used for evolving new varieties through hybridization. The size of the spike and the flower depends upon the size of the corms planted. A medium-sized corm (10-12 cm), with a high crown is better than a larger and flatter corm. The corms are planted about 15-20 cm apart in rows spaced 30-45 cm apart. Sometimes, they may be planted in clumps of three or four, particularly for mass effect or as borders. The depth of planting corms is about 10-12 cm. Deeper planting being adopted in a lighter soil.
In the nortern plains, it is best planted from September to October and sometimes even earlier in August. Flowering takes place from December to April. In the hills, planting is done in March-April and it flowers from June to September. The time of flowering depends upon the variety and the time of planting. Successive planting of suitable varieties will ensure continued flowering over a longer period.
MANURING. Gladiolus grows best in a bed which has been manured previously for another crop. It does not require heavy manuring or excessive nitrogen as this practice tends to deteriorate the quality of the flower spikes and the keeping quality of corms. The plants respond better to organic manure than to artificial fertilizers. After 6 to 8 weeks of planting, the plants may be fed with liquid manure, about once a week. An application of light soot water can also be given once a month or once a fortnight. At the time of emergence of flower spikes, a dressing of about 2.5-cm-thick layer of leaf-mould is beneficial in producing better flowers with stronger spikes and better development of corms.
WATERING. The plants may be watered weekly or fortnightly depending upon the weather. During winter frequent watering may not be needed.
EARTHING AND STAKING. After about 6 to 8 weeks of planting, the plants may be earthed up. After the emergence of flower spikes, they may be staked, so that the spikes do not fall down when there is a strong wind. However, staking is not necessary when the plants are grown closely or in clumps, and it is not needed in the case of miniature, butterfly or primitive gladioli. Care should be taken not to injure the leaves at any stage as the injury is harmful to the plants.
LIFING AND STORAGE OF CORMS. After flowering, when the leaves have turned yellow and have dried, the corms are lifted from the ground, preferably with a fork, and care is taken not to injure the corms while digging them out. After drying the corms thoroughly, they are put in paper bags, each with a few perforations for proper aeration or are wrapped up in sheets of newspapers, and stored in a cool and dry place or preferably in a cold storage room. The corms are best stored at 4.5o to 10oC and at 80-90 per cent relative humidity.
DISEASES AND INSECT PESTS. The commonest diseases are the Fusarium and Botrytis rots which cause the rotting of corms in the field and during storage. Botrytis rot occurs mainly in the hills. During storage, the corms are attacked by Aspergillus, Penicillium and other fungi, causing them to rot. In plants raised from disease-affected corms, the leaves turn prematurely yellow and flower spikes become stunted. It is not possible to control Fusarium and Botrytis rots easily with fungicides. However, to check the diseases, it is necessary not to grow gladiolus in the same beds every year, as the casual organisms are soil-borne.
The anti-biotic Aureofungin has been found to be effective in controlling the diseases of gladiolus. The corms should be planted after dipping them for one hour into 0-0.5 per cent Aureofungin solution. Two sprays of Aureofungin may be given to plants, one at the 6-leaf stage and the other 20-30 days before lifting the corms from the ground when the foliage is still green.
Thrips damage the leaves and petals by silvering them. They can be controlled by spraying the plants with Malathion (10 cc in 10 liters of water), once every fortnight or so. Caterpillars, which also injure the leaves and flower-buds may be effectively controlled by spraying the plants with DDT or BHC. It is useful to treat the corms with DDt or BHC (5%) dust and with Captan before storing them. The dusting of corms with naphthalene, about 30 g for every 100 corms and covering them with sheets of old newspapers or with gunny bags to retain the fumes may also be practiced before storing the corms.
