Forcing Bulbs for winter Bloom Indoors

Guide H-412

Esteban Herrera, Extension Horticulturist
Lynn Ellen Doxon, Extension Horticulturist

College of Agriculture, Consumer and Environmental Sciences New Mexico State University

This publication is scheduled to be updated and reissued 10/99.

You can enjoy the look of spring during winter by forcing bulbs to flower. Bulbs can be forced to bloom before their normal season by providing them a period of cold temperatures followed by a period of warm temperatures.

Tulips, hyacinths, daffodils, crocus, dutch iris, and other hardy bulbs1 can be easily forced. Select bulbs that are heavy and blemish-free; large bulbs are easier to force and produce larger blooms than small bulbs. For best results, select bulbs that were produced for forcing purposes. Number one bulbs are usually the best quality and are recommended for forcing.

COLD TREATMENT

Florist suppliers often have precooled hyacinth and crocus bulbs, which are ready for forcing. However, if the bulbs have not had a cold treatment, place them in pots and store them for 8-12 weeks in a cold frame, cool cellar, outdoor shed, garage, or other dark area with temperatures from 35-45 degrees F. Do not expose bulbs to freezing temperatures.

Use clay or plastic pots that are wide at the top and somewhat more shallow than standard pots. For growing bulbs in containers, use a growing medium that is light, well-drained, and well-aerated. Equal parts of sphagnum peat moss, vermiculite, and perlite make a good medium. Fertilizer is not necessary during cold treatment because the bulb contains its own food supply.

Do not crowd bulbs in the pot; leave about 1/2" between bulbs. Place bulbs with their tips level with the soil surface. Leave about 1" between the soil and the rim of the pot for watering. Water the potted bulbs generously before placing them in storage.

Label the pots clearly. Schedule removal from storage so you will have a succession of blooms throughout the winter.

A bulb's root system will develop during the cold storage period. In fact, one sure sign that pots have had sufficient cold treatment is that a good root mass has formed in the pot, as indicated by the ease with which the plant can be removed from the pot. Also, some roots may be growing through the drainage hole and top growth may be visible.

WARM TREATMENTS

When potted bulbs are ready to be brought indoors, provide the bulbs with a one-week period of cool temperatures (40-50 degrees F) and low light conditions. Then bring the pots indoors and place them where they will receive adequate sunlight and where night temperatures are no lower than 60 degrees F. Pots must be well watered at all times; keep them moist, but not wet.

CARING FOR BULBS AFTER BLOOMING

When blooms wither, gradually reduce watering, but give enough water to keep the foliage green. Apply a water-soluble fertilizer to replenish the bulb's food supply. The size of next season's blooms will depend on the bulb's growth during this period.

Forced bulbs may not flower the following season. However, they will bloom in future years if their foliage is allowed to mature naturally by planting the bulbs outside as soon as the danger of freezing has passed.

New Mexico State University is an equal opportunity/affirmative action employer and educator. NMSU and the U.S. Department of Agriculture cooperating.

October 1994
Las Cruces, NM
5C
Written: October 1994
Last Modified:
Placed on Server: Nov. 20, 1995