Asiatic and Oriental hybrid lily bulbs used for cut flower forcing can be forced on a year-round basis by using a combination of precooled and frozen-in bulbs. The number of cultivars available is constantly changing. Generally, the asiatics force in 8-10 weeks. Oriental and auratum lilies force in 12-15 weeks and are available until June 30th.
After being programmed, forcers should be prepared to plant bulbs immediately on arrival. If they must be stored, place them at 32-35 ° F. Storage at higher temperatures will cause desiccation of the bulbs which will result in fewer flowers per stem. Forcers should always check to be certain the bulbs are not seriously damaged or diseased. Do not store for longer than 10 days. DO NOT REFREEZE.
Planting and Spacing
The planting medium should be sterile, well drained and have a pH of 5.5 to 7.5 with pH 7.0 being preferred. Because some lilies can develop leaf scorch due to soil borne fluoride, the medium should not contain superphosphate or perlite. If ground beds or raised benches are used, be certain to sterilize them and be sure they are low in soluble salts. Leaching may be necessary. They must be well drained. Bulbs for cut flowers can be planted in ground beds, 8-10" deep raised beds or standard pots. Plant bulbs with at least 2" of planting medium above the bulb nose. This is necessary to develop stem roots.
Suggested Number of bulbs for Cut Flower Forcing in Beds or Raised Benches:
12/14 cm 6-9 per sq ft
14/16 cm 5-8 per sq ft
16/18 cm 4-6 per sq ft
18/20 cm 4-5 per sq ft
Because of their length and variation in stem strength, some cut lily cultivars may need wire support systems. If used, be certain the netting has holes large enough to accommodate easy cutting and removal of the flowers. Also, place the netting over the bulbs directly after planting.
Water the planting medium thoroughly after planting and then keep the medium moist but not wet.
Lilies require a medium to high Light (>2500 ft candle) intensity greenhouse, especially during the short days of winter. If shading was used during the summer, be certain to clean the glass thoroughly before winter. In most instances lilies respond to HID lighting during the winter months. This aids in reducing flower abortion and abscission especially with sensitive cultivars. Forcers who have low light intensity winters should seriously consider installing an HID lighting system for forcing cut lilies. When very high light condition occur (spring/summer), screening or shading is advised. Extremely high light intensities can reduce the length of the cut flower.
Use 55-63° F (13-17° C) night temperatures and not higher than 70° F (21° C) day temperatures. Avoid great fluctuations in temperature, because this can help to promote leaf scorch. Also, whenever possible, start Orientals at 59° F (15° C) for about 4 weeks. Later, Orientals can be forced at higher temperatures (63-65° F/17-18° C) than Asiatics. In general, Asiatic and longiflorum lilies take 30-35 days to flower after they reach the visible bud stage of development and Orientals take 50-55 days. Lastly, when seasonally warm temperatures occur, try to keep the soil and air temperatures below 68° F (20° C). Mulching of ground or raised bed and shading are advised. Ground or raised bed and shading are advised. Use a well ventilated greenhouse. Do not permit humidity to build up.
The bulbs themselves contain lots of stored food, and they should be able to support the plant until the shoot emerges. Recommendations suggest withholding fertilizer until the shoot is 4-6" tall. Some growers incorporate a 10-6-4 slow release fertilizer in the medium prior to planting. Suggested rate is eight pounds per cubic yard. Use a liquid fertilizer such as 16-4-12 at the rate of 200 ppm to help deepen foliage color. If a preplant fertilizer has been added to the soil, then just use the liquid fertilizer every two weeks.
Growing in the Summertime:
It is very important that the stem roots are developed before exposing the lilies to warm summer temperatures. Keep the planted bulbs for 3-4 weeks at or below 65°F to allow the roots to grow. This can be done in a bulb cooler or cool basement. Bulbs that have a poor root system will flower unevenly and have a lot of bloom dropping.
Marketing, Harvesting and Storage:
Forcers - as soon as the first flower has fully developed color, but is not open, the plants should be cut. Care must be taken not to damage the unopened buds during marketing. Whenever possible, lilies should not be stored.