I have a friend who is against forcing bulbs because, she says, “it isn’t natural.” Forcing simply means that you are exposing bulbs to warmth sooner than if they were growing outside, so I’m not sure it could be considered unnatural either. Most spring flowering bulbs, except paper white narcissus which don’t need a cold period, can be forced, including the smaller grape hyacinth, crocus, and scilla.
Forcing bulbs is easy; simply pot up your favorite bulbs in soilless potting mix, water them well and then put them in a cold, but not freezing, place for at least 15 weeks. Cool soil stimulates root growth, which continues until it gets quite cold. Warmth after the cool period stimulates top growth and flowers.
Using the correct soil is probably the most important part of forcing bulbs because they will not stand soggy soil. A soilless potting mix like pro mix is an excellent choice, or you can make your own with 2 parts compost, 2 parts sphagnum peat moss, 1 part vermiculite and 1 part perlite. Personally I find using pre mixed easier.
Fill the pot half full of mix, place the bulbs in it and finish filling around them. Do not compact the potting mix. Give them a good soaking to settle the mix and then add more if necessary. When finished the tip of the bulb should be just peeking out of the potting mix. Tulip bulbs should have their flat side toward the pot, because this is where the first leave will form. Label the bulbs clearly!
After potting I dig a trench just deep enough to sink the pots to the top of their rims and then pack leaves or straw loosely around the pots. Then I cover the pots and trench with a foot deep mulch of leaves or straw. Finally I cover everything with plastic or a tarp so it doesn’t get wet and become a big frozen together mass. After 15 weeks I pull back the plastic and mulch, grab a pot of bulbs, bring them inside and water them, set them in a cool spot until I see top growth, and then set them in a bright window.
You can also use an unheated shed, garage, crawlspace, or even a refrigerator. Many people put them in cold frames but the temperature can rise quickly on sunny winter days, so the top will have to be opened occasionally to keep the temperature at or below 45º F (7.2º C). Bulbs need cold but they shouldn’t freeze, so temperatures shouldn’t fall below 35 º F (1.6º C). Bulbs cooled in a trench should go in no later than November 15th for late February blooming.
When bulbs have finished blooming put them in the coolest, sunniest spot available and continue watering until they can be planted outside. It may take up to 2 years for the bulbs to produce large blooms again after they have been forced.
Tulip Potting Photo by Iowa State University Extension service
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