University of Illinois Extension

Forcing Spring Bulbs for Color

Even the dullest gray days of winter can be brightened up with colorful spring blooming bulbs grown indoors, said Susan Grupp, a University of Illinois Extension horticulture educator based in DuPage County.

“You can create an indoor garden with easy- to- force bulbs such as daffodils or hyacinths,” she said. “Coaxing the bulb to grow and bloom out of season is not difficult but requires special handling.”

Grupp recommended beginning by selecting large, high quality bulbs with no sign of mold or blemishes. Pay attention to varieties—some are easier to force than others. Check the labels for those recommended for forcing.

To plant, choose containers with good drainage. Shallow plastic or clay pots work well.
“You can use a store bought potting mix or make your own by combining 1/3 garden soil, 1/3 peat moss or leaf mold and 1/3 coarse sand or perlite,” she said. “Add one inch of gravel to the bottom on the pot, and then enough potting mixture to hold the bulbs so their tips are even with the pot rim. Set the bulbs firmly against the soil and space them so each bulb just touches the next. Crowded pots make beautiful arrangements. “

Continue by gently adding soil mix around the bulbs. Small bulbs such as grape hyacinth and crocus should be covered completely. Larger bulbs such as daffodils and tulips should not be completely covered—their tips should be seen.

Water carefully and label the pot(s) with the date planted and type of bulb, and expected date to begin forcing.

“The next step is to provide a cold treatment to encourage good rooting,” Grupp said. “Most spring flowering bulbs require about 12 weeks of chilling at temperatures maintained between 35 and 40 degrees (tulips need 14 weeks). Pots can be set in a cold frame, an unheated garage, a root cellar, or even a pit dug in the ground. Insulate the pots with straw and protect them from rodents using wire screening. If you use a refrigerator, wrap each pot with foil and check periodically to make sure it does not dry out. During this cold treatment, the soil mix should be kept moist but not too wet.”

After the proper cold treatment period has been met, the bulbs should have developed a good root system. At this time, you should see small yellowish leaf sprouts.

“Now you can force them into growth and bloom,” she said. “Move the pots to a cool area (60 degrees) with bright light. Do not place in direct sunlight. Water pots as needed. When shoots are about 2 - 3 inches tall, move them to a sunny, cool window. It usually takes 2-4 weeks for forced bulbs to bloom. Bring in a few pots every week for a continuous bloom.”

Grupp noted that forced bulbs should not be forced again (except amaryllis). If you plant forced bulbs outdoors, it may take 1-2 years before they bloom again.