5 Things to Know Before Forcing Bulbs

Welcome spring flowers early with these tips for successfully forcing bulbs indoors.

5 Tips for Forcing Bulbs

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Although it sounds rather aggressive, forcing bulbs for flowering plants is a lovely way to bring pops of springtime color to your home and banish the winter blahs. This horticultural magic trick involves fooling bulbs into behaving as if they’ve gone through vernalization, the chilling period that produces such blooms as tulips and daffodils. Temperature and timing are each key to the process, but even if you haven’t planned ahead you can still treat yourself to a bright, beautiful indoor spring garden now. Read on for the forcing bulbs 411.

1. Pick healthy bulbs.

The best bulbs for forcing are in firm fettle; squishy areas are a red flag. Also avoid bulbs with a powdery, grayish-green coating, which indicates mold has set in—a sign of weakness. Spring-blooming bulbs such as crocus, hyacinth, Dutch iris, Muscari, daffodil, and tulip tend to respond well to forcing. While nurseries sell the majority of these spring-blooming bulbs in September and October, which is prime time for outdoor planting, most big box stores carry paperwhites and amaryllis through the winter months. Since these tropical bulbs don’t require a chilling period, you can grow them at any time.


Forcing Bulbs of Tulips to Bloom Early

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2. Chilling lengths vary.

Spring bulbs require a cold snap to mimic the winter conditions of the natural environment in the ground, but the length of time spent in chill mode varies for different types of plants, so that’s where planning is crucial. Some bulbs, like hyacinths and tulips, require as many as 15 weeks to chill before they can be forced into bloom (timing that includes the two to three weeks it takes for the flower to develop indoors). While you’ll check the tag on the bulbs you purchase to determine the recommended chilling period, here are some chilling times for the more commonly forced bulbs.

  • Crocus: 15 weeks pre-chilling, two to three weeks to bloom after pre-chilling and planting, 17 to 18 total weeks
  • Hyacinth: 12 to 15 weeks pre-chilling, two to three weeks to bloom after pre-chilling and planting, 14 to 18 total weeks
  • Muscari: 13 to 15 weeks pre-chilling, two to three weeks to bloom after pre-chilling and planting, 15 to 18 total weeks
  • Daffodil: 15 to 17 weeks pre-chilling, two to three weeks to bloom after pre-chilling and planting, 17 to 20 total weeks
  • Tulip: 10 to 16 weeks pre-chilling, two to three weeks to bloom after pre-chilling and planting, 12 to 19 total weeks

If you haven’t planned ahead, bulb companies such as Tulip World sell pre-chilled bulbs. Though intended primarily for folks in southern states where the ground never freezes, these bulbs are a great option for those who want to force a few bulbs indoors during the winter but
missed the weeks-long chilling period.

Also, keep in mind that forcing bulbs isn’t an exact science. You may wish your blooms to be at their peak for a special occasion—as Easter décor or as a birthday or anniversary celebration, for instance—no matter how well you’ve planned, bulbs will flower when they’re ready.

3. Find the right place to pre-chill bulbs.

The ideal chilling temperature is between 35 and 45 degrees Fahrenheit. An unheated garage, root cellar, potting shed, shaded cold frame, or refrigerator are all ideal environments. (Note: If chilling bulbs in the fridge, stow them in a vegetable or crisper drawer away from other fruits and vegetables that release ethylene gas, which can impair flower development.) The goal is to keep bulbs not only cold but shielded from light during the process, so store them in a brown paper bag or covered loosely with newspaper. You can also chill bulbs in flowerpots, explained below.

4. There are three ways to chill and grow bulbs.

You’ve got three options for successfully forcing bulbs:

Potting, then chilling. Partially fill a flowerpot or other container that has good drainage with a potting mix. Use enough soils so that when bulbs are placed on top, their necks (the pointy part of the bulb) are at or just below the rim of the pot, and there are at least two inches below the bulb for root growth. Snuggle in tightly as many bulbs as will fit shoulder to shoulder; potted blooms look best crowded together. Fill in the areas between the bulbs with more potting mix up to their necks. Water thoroughly, but don’t drench the container—aim for damp, not sopping, soil. Cover the container with foil or newspaper secured with a bit of twine and let chill for the recommended period. Follow the steps in the next section once you’ve brought the container indoors.

Chilling, then potting. Once bulbs have undergone a chilling period outside a pot, pot them following the steps in the previous section. To get them growing, “wake” them gradually by placing the container in indirect light for the first two weeks. Once shoots are about three inches long, move them to a warm, sunny window. When color appears on the buds, move them out of direct sunlight to prolong bloom.

Forcing Bulbs of Hyacinth to Grow in Water

Photo: istockphoto.com

Chilling, then growing in water. You can purchase hourglass-shaped vases designed specifically for bulb forcing in water on Amazon or use any other container that’s at least as tall as the plants’ stalks at full height. If using a specialized bulb vase, fill it with water high enough so that just the base of the bulb is submerged; top off as need to keep the water at the right level. For other containers, simply fill the bottom with pebbles or decorative glass beads, add water so that it just covers the fill material then nestle the bulb into the pebbles so that only the roots are in contact with the water. Top off with water to maintain contact with the bulb as needed, ensuring that the rest of the bulb remains completely dry.

5. Make good use of post-bloom bulbs.

Why throw out a plant when blooming has ended? Most bulbs, after all, are perennial. While those living in areas where the ground doesn’t freeze should probably pitch forced bulbs and start fresh each year, cold climate dwellers can treat the potted greenery as you would a houseplant, keeping it watered, fed, and in bright sunlight. Remove the dead flower stalks and once the foliage turns yellow (a signal that the plant is ready for a rest); stop watering and feeding the plant and let the soil dry out, then transfer the container to a cool and dark location. Label each container with the name of the bulb so you’ll know what you have. Come autumn, dig out the bulbs and plant them outdoors in a sunny location where they’ll reap the benefits of rainfall and nutrients in the soil to grow stronger. With a little luck, they’ll return in the spring.