Forcing hardy bulbs to bloom indoorsMany fall planted, spring flowering bulbs may be grown indoors to bloom during winter.
Some of the most commonly indoor forced bulbs are small early tulip varieties, crocuses, daffodils, narcissus, and hyacinths. Pot these bulbs in a well-drained planting mix and containers with drainage holes. Plant the bulbs so that they are only half covered with potting soil. Allow for 2.5 cm (1 in.) or more of soil below the bulbs. For best results, plant bulbs with the same flowering times in the same containers.
Most hardy outdoor bulbs require a cool dormancy period at 3-10 C (35-50F) after they are potted. Use a cold room or an extra refrigerator for this purpose. Do not keep apples or cabbages in the same area since they release ethylene gas which will damage flower buds. These bulbs require total darkness during dormancy. Be sure to cover the bulb pots if they are located in an unheated porch or daylight-exposed area.
The length of the cool period varies depending on the type and variety of bulb. The cooling requirements for some of the popular forcing bulbs have been listed below to help you choose compatible bulbs.
During the cool period keep the soil barely moist. Check every week or so to make sure it does not dry out. If the bulbs are kept too wet the they can rot. Dust bulbs with Bulb Dust before planting or soak them in a Benomyl solution to prevent such problems. Benomyl also controls the growth of mould on the soil surface.
Once bulbs show signs of shoot development move them into a warmer brightly lit location at 15º C (60º F). Warmer temperatures may damage the flowers. Keep the soil evenly moist. After the buds appear, move the pots into any light for display. After blooming, bulbs may be discarded or saved for planting outside later in the spring. (They cannot be forced again.)
Hyacinths may be forced into special hyacinth glasses filled with enough water to touch the base of the bulb. They will still need to be cooled in water-filled glasses for 10-12 weeks.