By Megan Gross, Horticulture/Natural Resource Agent, Colorado State University Cooperative Extension
Many bulbs can be forced to bloom indoors in the winter. Look for bulbs that have been specifically bred for forcing or those that have been pre-chilled. Start with a clean container. An azalea container or a squat-shaped pot is better than a tall narrow container.
Use any good quality potting soil available at a garden center or nursery. Place 2 to 3 inches of potting soil in the bottom of the container. Place bulbs on the potting soil, but don't force them into place. Cover the bulbs with potting soil, leaving the tips exposed.
If they have not been pre-chilled, your bulbs are now ready for the chilling process. Pre-chilled bulbs need no additional chill period. The amount of chilling required varies with the type of bulb and cultivar, bulb size, number of bulbs per container and start date. Your local supplier can provide information about the specific cultivar you've chosen. Next, determine the bloom date you want and count backward. For example, early-blooming tulips can be forced to bloom before the first of February if they're started in early September. They need 14 to 20 weeks of cold preparation at 41 to 48 degrees, followed by two to three weeks indoors to force them to flower.
During the chilling process, don't let the bulb pans dry out or become too wet. Avoid storing bulbs in the same area as fruits and vegetables.
After you bring the bulb pans in from chilling, place the pots in indirect sunlight at 60 degrees for several weeks. When the plants are 4 to 6 inches tall, increase the temperature to 68 degrees. Do this through exposure to direct sunlight. Using these techniques, daffodils, narcissus, tulips, crocus, hyacinth, grape hyacinth and iris bulbs generally are easy to force in the home.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010