Once tulip bulbs are cooled, they have completed the programming phase of the forcing procedure and are ready for greenhouse forcing. This forcing stage takes approximately 1.5 to 4 weeks depending on the cultivar used, the season, and the temperature. In general, later crops take less time because they have been in the rooting room for longer and are at a more advanced stage of development than earlier crops. Also, prevailing greenhouse temperatures are important as well. Tulips may be forced at many different temperatures.
Little fertilizer is used because most nutrients come from the bulb.
There is a need for calcium supplements in the form of calcium nitrate to prevent stem topple from calcium deficiency. Stem topple is characterized by glossy water-soaked areas on flower stems followed by falling over of the portion of the leaf just above the lesions. Standard control for stem topple is 2 lbs. To encourage stretching, blackcloth, cheesecloth or newspaper may be placed on plants for a few days after removal from the rooting room, or sometimes flats are started under the bench and then moved to a raised bench. A-Rest plant growth regulator drenches are often used to keep stems short.