It may sound cruel, but forcing bulbs to grow indoors is a much kinder process than you’d think. In reality, the indoor gardening method should really be called “tricking bulbs.” By providing favorable climactic conditions indoors, you stimulate flower bulbs to bloom out of season.
Freelance garden writer Kathy Purdy of ColdClimateGardening.com gardens indoors during the winter months in Upstate New York. “What I like best about forcing bulbs inside is watching them grow over the course of weeks, all while it’s snowing outside with no possibility of watching plants grow there,” she says.
Through forcing, you may get beauties like hyacinth, paperwhite narcissus, and amaryllis to bloom in your home for the holidays. And even if they don’t cooperate, and end up flowering after the first of the year, that’s okay.
“For a gardener facing a long winter, forced bulbs are equally cheering in January, February, and even March, so if you don’t get them to bloom for the holidays, you’ll enjoy them when they do bloom,” says Purdy, who was surprised in March 2012 by an amaryllis she’d been coaxing to bloom that suddenly flowered and grew especially large.
Several bulbs can be forced indoors. Besides hyacinth, amaryllis, and paperwhite narcissus, you can enjoy the blooms of Soleil d’Or narcissus, Iris danfordiae, and Iris reticulata, as well as some varieties of crocus and tulips.
To force bulbs to bloom in your indoor garden, follow these steps.
1. Choose bulbs carefully. Pick bulbs that are large and firm and have no soft spots.
2. Provide chilling. Some bulbs require pre-chilling, including tulips, crocuses, and hyacinths. This should be done even if the bulbs indicate they’ve been chilled. Place the bulbs in the refrigerator in a paper bag and store them away from fruit, such as apples, which emit ethylene gas that can rot the bulbs. Chill the bulbs for at least 4 to 6 weeks.
3. Decide on a planting method. Bulbs can be forced over water or in potting soil, sand, or gravel. The container you choose will depend on how you’ll be planting. Hyacinth jars come in an hourglass shape and are used for forcing bulbs over water. For forcing in a planting medium, choose a shallow container without drainage holes.
4. Plant. Place water-forced bulbs tip-end up, with the bottom of the bulb 1/8th to 1/4th of an inch from the water’s surface. Roots will grow into the water. Use water forcing for crocus, hyacinth, and narcissus.
All bulbs can be planted in soil, sand, or gravel. Position them tip-end up, with ½ to ¾ of the bulb covered with planting medium. For a good color display, pack the bulbs shoulder to shoulder.
5. Place bulbs in a cool, dark area for 2 to 3 weeks. They will form a strong root structure. Hyacinths require 6 to 7 weeks. Good locations include dark, unheated spots like a basement or garage.
6. Remove bulbs from darkness when they have 4 to 6 inches of growth or when the forcing vase is filled with roots. Place them in a dimly lit location for another week and then transition to an area with medium light, at which point they should start to bud up. After the foliage has greened and the buds have swelled, place the arrangement in its final destination in a bright location away from direct sun and heating vents.
7. Water bulbs grown in planting medium when the first inch of medium dries out. Keep bulb vases filled with water, but avoid letting water touch the bottom of the bulbs.
8. Figure out bloom times. Forced bulbs generally flower from 4 to 16 weeks after planting. Paper-whites bloom in 4 to 6 weeks, hyacinth in 12 to 16 weeks, amaryllis in 8 to 12 weeks, and crocus in 6 to 12 weeks.