How to Force Bulbs Indoors for Winter Blooms
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- 4 min read
Forcing bulbs allows you to enjoy bright flowers indoors during winter and spring by simulating outdoor conditions. The process includes selecting suitable bulbs, planting them in well-drained containers with proper orientation and spacing, providing a cold period and then relocating them to warmth for blooming. Careful storage and handling, correct planting techniques and attention to timing are key to successful blooms.
Selecting and Storing Bulbs
Choose bulb varieties suited for forcing, like tulips, daffodils, hyacinths and crocuses. Store unplanted bulbs in a mesh or paper bag in a refrigerator or cool location (35-55°F). Keep bulbs away from ripening produce, as ethylene gas released by produce can cause bulbs to rot.
Planting Your Bulbs
The optimal period for planting bulbs extends from mid-September through December, contingent on the desired bloom time. For blossoms in late December, plant in mid-September; for February blooms, plant around mid-October; and for displays in March or April, mid-November is recommended.
Procedure for Planting Bulbs:
Use clean containers with drainage holes. If using clay pots, soak them overnight to prevent them from pulling moisture from the soil.
Prepare a well-draining mix of equal parts potting soil, sphagnum peat moss (or an alternative, such as vermiculite) and perlite. Fertilizer isn’t necessary because bulbs have stored nutrients for growth.
Loosely fill containers with soil mix. Leave tips of large bulbs (e.g., tulips, daffodils) exposed; fully cover small bulbs (e.g., crocus, snowdrop and grape hyacinth). Keep soil loose for healthy root growth.
Space bulbs according to pot size: six tulips, three hyacinths, six daffodils or 15 crocuses in a six-inch pot. Position tulip bulbs with the flat side facing the pot edge for even leaf arching.
Add soil to ¼–½ inch below the rim. Water until it drains from the bottom, then label pots with cultivar, planting date and indoor-forcing date.
Cooling the Bulbs
Most hardy bulbs require 12–16 weeks of cool temperatures, between 35 and 50°F. This stage supports root development and stem growth and helps avoid short stems or incomplete flowering. If bulbs have been refrigerated for over three weeks before potting, subtract that time from the overall cooling requirement. Appropriate cooling locations include an unheated basement or crawl space, or a refrigerator.Â
Below is a reference table from the University of Wisconsin Horticulture Extension outlining the cold period required for each bulb type to achieve successful forcing.
Forcing Blooms
After chilling, bring bulbs to warmth and light:
Place pots in a cool spot (60-65°F) with indirect sun.
When shoots green up, gradually increase warmth and light.
Rotate pots for even leaf growth.
Flowers should appear in three to four weeks; move to indirect sun when buds show color.
Keep soil moist. At night, place pots in a cool room to extend blooms.
What to Do After Forcing
Hardy bulbs that have been forced can be planted in the garden once spring arrives. Alternatively, you can allow them to mature and go dormant in their pots before planting them in the fall. Daffodils can be transplanted in the spring. They may not flower the following year, though they might bloom the year after. Tulips, paperwhites and hyacinths are generally best composted after forcing.
Forcing Paperwhites and Amaryllis Without Cooling
Paperwhite and amaryllis bulbs do not need a chilling period before blooming indoors because they are adapted to warmer climates and have physiological traits different from spring-flowering bulbs that require cold exposure. Paperwhites and amaryllis flowers bloom with the right amount of warmth, light and water.
Paperwhites (Narcissus tazetta)
Paperwhites can produce indoor blooms from Thanksgiving through late March.
Procedure for Forcing Paperwhites:
Choose an undrained decorative bowl or dish with at least two to three inches of depth and fill it with pebbles, pea gravel, coarse sand or pearl chips, leaving about one inch at the top.
Add water until the water level is just below the surface of the gravel.
Place the bulbs on top of the gravel and secure them by covering the bottom quarter of each bulb with more gravel.
Monitor water levels carefully; excessive moisture can lead to bulb rot.
Place tender narcissus varieties in a cool environment (50-60°F) with low light for two to three weeks, or until they become well-rooted and shoots emerge. Gradually transition the plants into direct sunlight and warmer conditions thereafter.
Paperwhite bulbs are not suitable for re-forcing and should be composted post-bloom.
Amaryllis (Hippeastrum cultivars)
Amaryllis bulbs can be successfully forced indoors within four to six weeks, without a cooling period.
Procedure for Forcing Amaryllis:
Amaryllis bulbs are sold individually or as kits with a pot and soil.
Choose a pot about one inch wider than the bulb and fill it with fresh soil.
Plant so the top quarter of the bulb stays above the soil surface; press the soil gently to remove air pockets and secure the bulb.
Add gravel for stability and to ensure good drainage. Amaryllis roots should not sit in water.
Water around (not on) the bulb, place in bright light (east- or south-facing), and expect blooms in four to six weeks.
After flowering, bulbs can be transplanted outdoors in spring or kept in pots for ongoing growth.
References and Further Reading
Writer Biography
Elizabeth Lorentz gardens at Mears Park in downtown Saint Paul. She loves cooking
and growing native perennial plants and herbs. She is a Master Gardener with the
Ramsey County Master Garden Volunteer Program.
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Photo Credit: Nika BenedictovaÂ