How to Force Bulbs Indoors
Many bulbs can be forced or stimulated to bloom indoors in the winter. Look for bulbs that have been specifically bred for forcing, or those that have been prechilled. Start with a clean container. An azalea container or squat-shaped pot is better than a tall, narrow container.
Use any good-quality potting soil available at your favorite garden center or nursery, but don't use fertilizer because it will increase salt content. Place approximately two to three 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 planted bulbs leaving the tips exposed.
Your bulbs are now ready to be chilled. The amount of chilling required varies with 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 chosen. Next, determine the bloom date and count backwards. For example, early-blooming tulips can be forced before February 1, if they're started in early September. They need 14 to 20 weeks of cold preparation at 41 to 48 degrees Fahrenheit, followed by two to three weeks indoors to force them to flower.
Don't let the bulb pans dry out or become too wet while chilling. Avoid storing bulbs in the same area as fruits and vegetables. Ripening vegetables and fruit, like apples, give off ethylene, which can cause flower-bud development to fail.
After you bring the bulb pans in from chilling, place the pots in indirect sunlight at 60 degrees Fahrenheit for several weeks. When the plants are four to six inches tall, increase the temperature to 68 degrees Fahrenheit through exposure to direct sunlight. Daffodils and narcissus, tulips, crocus, hyacinth, grape hyacinth and iris bulbs are generally easy to force in the home using these techniques.
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Updated Tuesday, October 13, 2015