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Horticulture: Crop Plantation Guidence

Bulbs

Introduction

In horticulture, the word bulb includes underground modified stems which are used for propagation e.g. bulb, corm, tuber and rhizome. Plants with tuberous roots are also grouped as bulbous plants. A large number of these plants producing attractive flowers are grown in the hills and are commercially grown well both in plains and hills but the season of growth and flowering may vary. A bulbous plant has normally three phases during a year growth, flowering and dormancy. Vegetative growth may precede flowering as in Gladiolus or flowering starts before the leaf emerges, e.g., Amaryllis, Haemanthus. After growth and flowering, the plants in most cases, enter into rest period and the duration of dormancy varies with the type of plants and environmental conditions like temperature and humidity.

Bulbs which grow and flower well in the hills include Agapanthus, Anemone, Cylamen, Eurycles, Fritillaria, Iris, Ixia, Hyacinth, Moraea, Montbretia, Nerine, Paeonia, Kniphofia, Ornithogalum, Ranunculus, Tulip, Watsonia, Sparaxis, Zantedeschia Tuberous Begonia, etc. Although some hardy types of Freesia, Daffodil, Narcissus, Gloxinia, and Lilium may flower in plains but they do not show very attractive display of colour and often fail to flower in the second year.

Planting

Bulbous plants are grown in beds, shrubbery, herbaceous border, and grassy land and in pots and bowl. Bulbs, corms, rhizome or tuber are usually planted when they have shown signs of sprouting after dormancy. In Canna, however, the rhizomes are taken out of bed in growing condition and replanted after a week or so. The planting materials are normally placed deep in the soil and the soil around it is gently pressed. The depth of planting varies with the type of plants and size of bulbs. For most of the bulbous plants grown in tropical garden, the planting depth is between 3-10cm.Bulbs are used for vegetative propagation. Various methods and structures used for propagation are as follows:

  1. Division of clump – Rhizomatous plants like Canna, Alpinia can be divided into small clumps.
  2. Offsets produced laterally are separated for multiplication.
  3. Cormlets or bulblets produce new plants.
  4. Scales of Lilium are separated and used for propagation.
  5. Bulbil arising from the axils of leaves produce new plants.
  6. Pieces of bulb disc with leaves or rhizome also develop new plants.

Soil

Soil should be sandy loam or loamy sand in texture for better production of bulbs. It should be moderately fertile with good water holding capacity and with pH ranging between 7.0 – 8.0. For pot culture the ideal pot mixture should contain 2 parts sand: 2 parts leaf mould: 2 parts well rotten farmyard manure: 1 part soil and part charcoal. Bulbs prefer loam or sandy loam soil. In stiff clay, rooting is delayed and too much moisture often causes rotting. If the soil is not perfectly well-drained, the bulbs may be planted on a bed of sand. Watering is not required after planting as the fleshy underground stems contain sufficient food materials to develop initial growth of root and shoot. Before root formation, watering proves injurious to the bulbs and helps in rotting.

Climate

In general, cool weather, high atmospheric humidity and moist soil conditions are congenial for the manufacturing of food, better production of high quality flowers and bulbs. According to climatic requirement of these bulbs, they are grouped into two categories i.e. Warm climate – Gladious, Narcissus, Daffodils, Freesia, etc. Modified environmental conditions are to be provided during winter and summer seasons for the production of high quality blooms. Most of these plants prefer sunny situation, while Eucharis, Zephyranthes thrive better in semishade; few types, e.g. Pancratium, Haemanthus, Zephyranthes grow and flower well in sun and semishade. Bulbs, corms and tubers should not come in direct contact with fresh organic manure, rhizomes are not usually affected.

Manuring

Well rotten farmyard manure @5kg/sq m should be incorporated at the time of soil preparation. The application of 20g each of P2O5 and K2O/sq m has also been found beneficial at the time of planting bulbs. Nitrogen @40g/sq m into two-three splits should be applied.

Intercultural operations

Weeding and hoeing

Weeds should not be allowed to grow and should be removed as soon as they appear otherwise they compete for nutrients and water with the main crop. Hoeing helps in aeration of soil and better development of bulbs. In early stages of growth frequent weeding and hoeing are required.

Irrigation

Liberal application of water at all stages of development is highly beneficial. Generally 7-10 days interval is appropriate in winter whereas in summer it should be about 5-7 days.

Staking

Bulbous plants like Gladiolus, Dahlia, Lilies, etc. produce flowers on long stem and thus need support. Otherwise spiks may bend down and break with strong winds. Bamboo stakes can be provided.

Harvesting of flowers

The stage of harvesting of flowers depends upon the distance of travel. It varies with the kind of flower. For local market, gladiolus and tuberose should be cut when lower 2-3 florets have opened. Whereas for distant market, flowers are cut when basal florets show colour. Narcissus and Daffodil are cut at goose neck stage. Before harvesting the flowers, plants should be irrigated.

Lifting of bulbs and their storage

Tender bulbs like Gladiolus, Dahlia, Narcissus, Daffodils, etc. are to be dug from the soil 10-12 weeks after flowering has been finished. Before lifting the bulbs, water is withheld. After digging, bulbs are dried in shade for few days. Then these are treated with 0.2% Bavistin solution for 30 minutes and thereafter stored. Hardy bulbs are separated after 2-3 years and are again planted in the planting season.

Time of planting depends on the season of flowering, environmental condition of the region and condition of the planting material. In the plains, Gladiolus is planted from September to November, whereas in the hills, the planting season is normally from April-June. Amaryllis, Hippeastrum, Harmanthus are planted in January-February to obtain flowers in March-April. Caladium and Canna are put in the ground in May.

Lifting and storage

After the above ground portion dries out the bulbs are lifted out carefully. The root and shoot are cut and the bulbs are cleaned before storage. They should be stored in dark, dry and airy place until the time of next planting. Storage condition is very important for obtaining healthy bulbs. If the humidity is very high, fungus develops on the bulbs and causes rotting. In a very dry atmosphere the bulbs shrivel and may lose viability. It is necessary to lift all types of bulbous plants every year. Amaryllis, tuberose, Caladium, Pancratium, Zephyranthes may remain in the ground for three years before they are lifted. But water should be withheld when the bulbs are lying in dormant condition in ground or pot. Gladiolus, on the other hand, has to be lifted out every year after drying of leaves.