A wide range of tulips is grown both for bowl culture and for cut flower production in boxes or greenhouse borders. The flowering times of a tulip and the ability to force it to flower early depends on a range of temperature treatments best left to the suppliers, as wrong treatment will result in the production of deformed flowers. In recent years specially prepared bulbs called 5° tulips have been used to a large extent for cut flower production in greenhouses.5° tulips
Initially for two weeks the soil or growing medium must be kept cool, in the region of 10-12.8°C (50-55°F). 5° bulbs of a 12cm size are generally planted direct into greenhouse borders with a pH of 6.5 to 7 during the first week of late autumn in rows 15cm (6in) apart, the bulbs being 5cm (2in) apart, with the top of the bulb 1 cm (1/3in) below soil level. It is usual to grow in beds for easier management. After planting, the beds are thoroughly watered, not only to settle the soil but also to reduce temperature, but water-logging should be avoided. Heat is given after 2 weeks, up to 17.8°C (64°F) air temperature, and at this temperature flowering occurs. For later flowering a lower soil temperature, 10.6-11.1°C (51 — 52°F), is necessary for two weeks, then raise air temperature to about 15°C (50°F), a procedure which will keep flower quality high. Ventilation should, however, be given to avoid excess humidity and possible spread of botrytis.Pre-cooled tulip bulbs
These are usually grown in boxes, the bulbs being planted in early October according to their size (generally 11-12cm or larger) from 6 x 11 (66) up to 13 x 7 (91). Boxes should be 7.5-10cm (3-4in) deep, clean and provided with adequate drainage. Soil should be of good texture with a pH of 6.5-7 and should not have been used for bulbs beforehand. Fill to within 2.5cm (tin) of the top and press the bulbs into the surface, adding more soil to leave the nose of the bulbs exposed. A layer of sand or ash is then put on top of the boxes to form a barrier between bulbs and plunge soil.Boxes are then stacked in rows out of doors and covered with a layer of 15cm (6in) sand or peat, and straw on top of this. The watering of the straw subsequently induces the cool conditions necessary by evaporation. Fungal dusts (quintozene) are useful before the bulbs are covered by the soil.
After being in the plunge for a minimum period of 6 weeks, bulbs are brought into the greenhouse when the flower bud is clear of the neck of the bulb (as can be determined by examination) and there is good root growth, the temperature then being raised gradually to 21.1°C (70°F). They should be given shading by newspapers or other means to draw the flower up, or alternatively by putting them under benches. Temperatures are dropped as buds show colour.
Tulip bulbs can be brought into the greenhouse in succession to flower over a period, flowering commencing in early winter. It is important, however to pay attention to the programming provided by the supplier. Uncooled bulbs are given the same general treatment for flowering from mid-winter to early spring.
Pot culture
Bulbs being grown for pot display are generally of the more dwarf varieties of early singles and doubles. They are planted up closely and fairly firmly in pots or bowls of various sizes, either in bulb fibre or clean soil in mid-autumn with the nose of the bulb exposed. The bulbs may be plunged into a deep layer of soil or peat and put into a dark cupboard and after the necessary 6 week period brought into the greenhouse or a warm room where once again shade is essential to begin with. At all times where bulbs are being grown in boxes or pots, adequate water supplies should be maintained, but never to the extent of spotting the blooms by careless over-application. Gardeners frequently find that gross foliage and weak flowers result, this being due in the first case to an insufficiently cool rooting period, and latterly to excess temperatures applied too quickly.There are many variations of tulip culture, including the use of mobile greenhouses, when the bulbs planted out of doors can be brought forward to flower earlier than the outdoor crop by covering in early spring.
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