Greenhouse Bulbs – Lily of the Valley and Muscari
Lily of the valley (Convallaria majalis)
These are produced from imported ‘pips’, generally from Germany. Of the three grades available, only three-year or two-year top grade pips should be used. For very early flowering it is necessary to retard the pips from 10-12 weeks at —4°C to —2°C (28-25°F) treating them as bulbs, thawing them out in a warm bowl of water at 26.7°C (80°F) for 12-15 hours. The retarding will generally have been carried out before purchase.
The pips should have their roots trimmed down to 8cm (3in) before planting in 13cm (5in) deep boxes or in a bed of similar depth, using a mixture of peat and sand. They are spaced 2.5-5cm (1-2in) apart, being covered finally by a layer of damp peat. Complete darkness is necessary for the initial forcing process for 10-12 days, which will necessitate the use of a shaded greenhouse bench (using black polythene covers) or a shed. Bottom heat to the 21.1°C (70°F) level is necessary, and this can readily be provided bywarming cables, with an air temperature of 15.6°C (60°F) for the first three days, 21.1°C (70°F) for the following three days and 26.7°C (80°F) for the remainder of the forcing period. The pips are thoroughly watered-in on planting and watered again in 10-12 days. When shoots appear in 10-12 days the shading is removed. When they are 30cm (12in) long artificial light is given, to provide 16 hours of light and 8 hours of complete darkness until the are ready for cutting. The lighting can be achieved by 100W tungsten filament lamps at 1 per m2/ sq yd, 60cm (2ft) above the beds. Too strong a light or light given too soon will restrict stem height. Temperatures are reduced when cutting commences.
Muscari armeniacum or grape hyacinths are useful flowers for greenhouse culture, both in bowls and for cut bloom. Specially prepared can be obtained, although in gardening circles the late flowering of unprepared bulbs is usually more acceptable.
For forcing, the bulbs are planted in 7 .5 — 10cm (3-4in) deep boxes in early to mid-autumn, plunged out of doors for a period, and then brought into the greenhouse to flower. More usually, however, they are planted 2.5cm (tin) apart in pots or boxes and kept cool 4.4-7.2°C (40-45°F) for eight weeks or longer, when they arc brought into flower in a moderately warm greenhouse.