Forcing Bulbs Indoors

Many of the fall bulbs that normally bloom in the spring can be “forced” to bloom indoors over the winter. The term forcing is used because the bulbs are manipulated to bloom earlier than their usual schedule. In order to do this, they need to experience a cold and dark period to mimic natural dormancy. The best bulbs to use for this purpose are tulips, daffodils, hyacinths, crocus, grape hyacinths, species iris, and scilla. Try to choose varieties that are shorter, so they are less likely to flop over.

Planting

Planting bulbs in soil is the easiest way to force bulbs. Plant the bulbs in a shallow container, close together, and just below the surface of the soil, so the tip of the bulb is showing.

Care

Water and set in a dark, cold place for 8-16 weeks. Ideally the temperature should be 40-48 degrees F, so an unheated basement or garage is usually perfect for this. They can be placed in the refrigerator, but not if there is any fruit present, as fruit releases ethylene which can spoil the bulbs. Avoid freezing temperatures, and keep soil evenly moist but not wet.

When top growth appears, bring it into a cool spot (50-60 degrees F) with low light for a week or two. Then move it to a brighter spot with indirect light, while keeping it relatively cool as the buds develop and bloom.

After they’ve been forced, it’s difficult for bulbs to recover, if they do at all. It’s best to treat these bulbs as annuals, and dispose of them when they’re finished blooming.

Required Cooling Period for Bulbs
Species Iris 6-8 weeks
Scilla 8-9 weeks
Grape Hyacinths 8-9 weeks
Crocus 10-12 weeks
Hyacinths 10-12 weeks
Daffodils 12-13 weeks
Tulips 14-15 weeks