If you’re the type of gardener who spends the winter months anticipating the first flowers of spring, you might want to try “forcing” bulbs. By providing favorable conditions indoors, you can trick many bulbs into blooming during winter well before they would normally flower outdoors. The technique is called forcing, which stimulates a plant to bloom out of season.
Though the effects are stunning, forcing bulbs is really quite easy. By controlling the climate, you create an environment that causes the bulb to bloom earlier.
Now, when bulbs are plentiful at nurseries, is the time to make your selections for forcing, said Marty Bailen, a nursery salesman at Rogers Gardens in Corona del Mar.
“We have a great selection of bulbs now,” he said. “For forcing, you want the biggest bulbs possible because they’ve stored the most energy and will give you the best show.”
Forced bulbs not only light up the house when there’s not much growing in the garden, but some are also fragrant.Containers of forced bulbs also make an inexpensive yet impressive holiday gift, Bailen said. And forcing is a fun activity for children, who can check on the bulbs’ progress each day.
Several types of bulbs can be forced indoors, though paper-white narcissus, hyacinth and amaryllis are by far the easiest, Bailen said.
If you’re looking for holiday bloomers, paper-whites and South African varieties of amaryllis are the most reliable, said Dan Davids of Davids & Royston Bulb Co. Inc. in Gardena, a wholesale bulb company that distributes to nurseries in Southern California.
Other bulbs that may respond to forcing include some varieties of crocus and tulips, Chinese sacred lily (Narcissus tazetta), Soleil d’Or (Narcissus tazetta), Iris danfordiae and Iris reticulata.
Bulbs are self-contained plants that store energy inside of themselves to produce flowers. When you force a bulb, you cause it to use up its food reserve.
Generally, a bulb that has been forced has used up its food supply, Davids said. “It probably won’t come back again, so the general recommendation is to discard most forced bulbs,” he said.
There are two methods for forcing bulbs, both fairly simple. Water forcing can be used to grow hyacinth, narcissus or crocus. Place the bulb in a conical container, above the water line. Roots grow toward and into the water, and the bulb sends up shoots and flowers. Bulbs in direct contact with water will rot.
Another method of forcing is to plant the bulbs in a pot of pebbles, sand, vermiculite or perlite. These mediums don’t provide nutrients but hold the plant upright.
All types of bulbs can also be forced in potting soil. Bulbs such as amaryllis require soil-forcing rather than water-forcing to successfully bloom out of season.
How long forced-bulb blooms last will depend on the type of bulb. Some, such as amaryllis, will last two to three weeks, while paper-whites often last a month and hyacinth blooms two to four weeks. Tulips are short-lived, lasting just a week.Keep the following simple guidelines in mind.
* Choose bulbs that are large and firm, Bailen said. Reject any that are soft, as they will probably rot during forcing.
If you’re unsure about what bulb varieties are good for forcing, ask a nursery worker for assistance. Just about any bulb can be forced, but many aren’t very successful at it. Flowers may be poor, or the stems may be too floppy for a heavy flower head and will simply lie over the sides of the pot.
* Some bulbs must be pre-chilled before forcing. Pre-chill hyacinth, crocus and tulips, Davids said. Place them in a paper bag, or a plastic bag that has holes, and put them in the vegetable crisper drawer of the refrigerator (away from fruit such as apples, which will release ethylene gas that can cause the bulbs to rot).
“Don’t skimp on chilling,” said Davids, who suggests chilling bulbs at least four to six weeks. “If you don’t chill certain bulbs enough, they won’t grow very tall.”
* Select an appropriate container. If you will be forcing a bulb over water, purchase a hyacinth vase or similar container that has an hourglass shape. This allows you to fill the bottom with water and set the bulb on top, above the water but not touching it.
When forcing in sand, vermiculite, perlite or potting soil, choose a container that is wide and shallow and doesn’t have drainage holes.
Terra-cotta bulb planters are good choices because terra-cotta breathes and will allow excess water to evaporate.
* To plant water-forced bulbs, place them tip-end up, one-eighth of an inch to one-quarter of an inch from the surface of the water but not touching it. If water-forcing in pebbles, embed the bulbs tip-end up so that half to three-fourths of the bulb is covered, Davids said. For bulbs planted in soil, sand, vermiculite or perlite, set them tip-end up with half to three-fourths of the bulb covered. Water the medium until it is thoroughly dampened but not soggy.
* When forcing over water, prevent a sour smell by adding a small amount of activated charcoal to the water. If you don’t like the look of charcoal, simply change the water every few days, Davids said.
* Create a big color display by packing bulbs in containers so that their shoulders are touching.
* Once planted, the general recommendation is to place bulbs in a cool, dark area while they form a strong root structure.
“Place most bulbs in a garage or basement for two to three weeks, and six or seven weeks for hyacinth,” Bailen said. You can remove the bulbs from darkness when they have 4 to 6 inches of growth on them, or when forcing in a vase, when the vase has filled with roots.
After removing them from darkness, place the bulbs in a dimly lit area for about a week and then move them into a medium-lit area for another week or so. Once they have greened up in two to three or four weeks, you can place them in their final destination, which should be a bright location.
Davids, however, counters this conventional approach. He believes that placing the bulbs in a cool, dark area is unnecessary.“We can break the rules here,” he said. “I’ve found that in our mild climate, it really doesn’t make a significant difference if you skip this step.”
Instead of placing bulbs in a cool, dark place indoors, Davids suggests starting them outdoors in the shade and then exposing them to sunlight when they have 3 or 4 inches of top growth. Once they green up and grow 3 or 4 inches more, bring them indoors.
“Although starting them outdoors tends to be slower, it creates stronger plants,” Davids said.
* Forced bulbs can be placed in most areas of the house. A bright room is a good location, but avoid putting them in direct sun, which can cause colorful flowers to fade faster.
Avoid uneven light, which will cause flowers to bend toward the light. And don’t place them in front of a heater vent, which will dry them out, or near a door that leads outside, where they can be exposed to drafts and temperature changes.
* Care for your forced bulbs. Water as soon as the surface of the planting medium dries out or, for those growing over water, when the bulb is no longer near the water’s surface. Bulbs will need the most water during blooming, but they may also need watering when they are forming roots.
Not much other upkeep is involved. Once the blooms are spent, the bulbs are finished and should be discarded. They will not bloom more if clipped.
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Bloom Times
Forced bulbs will flower anywhere between four to 16 weeks after planting, depending on the bulb type. Many bulbs can be forced now and in the next several weeks for blooms throughout the winter holiday season and into the new year.
Following are times from planting to bloom. They are approximate and will vary according to growing conditions:
Amaryllis (South African varieties): 8 to 12 weeks.
Chinese sacred lily (Narcissus tazetta): 6 to 12 weeks.
Crocus: 6 to 12 weeks.
Hyacinth: 12 to 16 weeks
Iris danfordiae or Iris reticulata: 12 to 16 weeks.
Paper-whites (Narcissus tazetta): 4 to 6 weeks.
Soleil d’Or (Narcissus tazetta): 6 to 12 weeks.
Tulips: 12 weeks.
