Big, Bloomin' Bulbs in Winter!

Coaxing spring-flowering bulbs to bloom during the winter is a popular trick for adding brilliant color to the home and a welcome boost to the spirit. Unfortunately, the trick does not work well for everyone, while even successful practitioners often look at the faded foliage and wonder what next?

The process of "forcing" bulbs simply means inducing plants to bloom ahead of schedule and out of their normal environment. This horticultural chicanery can be applied to almost any bulb, corm, or tuber, although the easiest subjects for beginners are generally paperwhite narcissus, fragrant hyacinth, large-flowering crocus, and amaryllis, the largest, showiest, and most versatile of the lot.

Other, slightly more difficult species include muscari, like grape hyacinths, colchicum, such as autumn crocus, snowdrops, freesia, and sweet-and- spicy Lily-of-the-valley.

Tulips and traditional garden daffodils are a bit more finicky, requiring better temperature control, brighter lighting, and so on, although many catalogs and gar- den centers will advertise some species more suitable for forcing, such as miniature hybrids that are more at home on windowsills.

Paperwhites (Narcissus tazetta) are especially popular, as they can be planted in either a light, porous soil mix or, more commonly, in shallow glass bowls or other attractive planters, using nothing more than a layer of water in clear or colored marbles, or pastel-tinted gravel, easily found at aquarium stores.

These narcissi are noted for their thin, delicate foliage and clusters of fragrant white flowers. Some indoor gardeners will plant clusters of five, seven, or more bulbs every two weeks or so to ensure an ongoing aromatic display throughout the holidays and late winter months.

Regrettably, these easy-to-grow paperwhites are native to the Mediterranean, and are not tolerant of our colder climate. Except for gardens in warmer zones from nine onward, the usual advice is to discard the bulbs. Personally, I would prefer taking a chance on planting them outdoors after the foliage has yellowed and died-back, rather than merely adding them to a compost pile. At any rate, the bulbs will have exhausted their energy reserves and cannot be saved for forcing again the following year, which is true of almost all forced bulbs.

On the other hand, you might try forcing a related narcissus species called Grand Soleil d'Or, which offers a deep yellow color with somewhat smaller clusters of blooms. These narcissi can be transplanted to your garden later in the fall and should provide a decent showing the following summer, improving each year thereafter.

The key to success with forced bulbs is keeping your cool - or, at least, keeping bulbs cool while they are rooting. And while there is a whole science to buying and storing bulbs in refrigerated conditions, any number of retailers offer "hardened- off" bulbs which have gone through the appropriate chilling process and are ready for forcing.

With these ready-to-go bulbs, you can select a number of planting options. Hyacinth or forcing jars are specially designed glass vessels appropriate for crocus, narcissus, or, naturally, hyacinths, which artfully support the entire bulb, allowing the roots to dip down into the water below. You can also employ a gravel medium for paperwhites, crocus, or colchicum, or plant them in a soil mix. For these and all other bulbs, use a shallow "bulb pan" with a loose potting medium of equal parts of soil, compost or peat moss, and vermiculite or perlite. Many bulb fanciers like to add a pinch of bone meal per bulb. A four-five inch pot works well for larger single bulbs like hyacinths, while a six-ten inch pot accommodates several large bulbs or a dozen smaller bulbs.

Keep species forced in water or set in gravel in a cool, dark room (ideally below 50 degrees F.) for at least several weeks, until the root system has become thoroughly established and the top shoot or stems start to elongate.

Soil-planted bulbs will also require cold storage at 35-48 degrees F. while roots are developing. Never allow bulbs to freeze, and keep the temperature below 55 degrees. The best locations are usually an unheated cellar, enclosed garage, insulated cold frame, or refrigerator. In a refrigerator, it is best to cover the pot with a plastic bag punched with several holes for ventilation. Keep the planting medium moderately moist. The length of chilling time required depends on the species, but usually averages 12-16 weeks. The longer the bulbs remain cool, the taller and fuller their flowers will be.

A fundamental mistake in forcing bulbs is skimping on the cold treatment. Often if bulbs fail to bloom, it is an indicator that the retailer did not allow the bulbs to remain dormant long enough, the bulbs were stored at too high a temperature, or the forcing temperature was too high.

After the bulbs have been chilled appropriately, move them into a somewhat warmer room (50-60 degrees F.) with indirect light for a week or so, until shoots or stems elongate and the buds begin to swell. It is now safe to move the pot into a bright window at normal indoor temperatures.

To keep the blooms for the longest possible period of time, it helps to move the pot into a cooler room in the evening and avoid direct sunlight.

After your bulbs have finished blooming, cut off the flower stalk above the base, but not the leaves! Treat your forced bulbs like a typical indoor plant, with bright light, periodic watering and fertilizing, all of which will help the bulb renew its energy stores for future growth and blooming.

Do not remove the foliage as it begins to yellow and wither, but do reduce watering significantly until all of the leaves have died back. At that point, as your bulbs enter their dormant phase, you should allow the soil to completely dry out, and either save the bulbs in their pots or, especially in the case of water-forced species, remove the bulbs or corms, gently rubbing them clean with a dry cloth, and store them in a cool, dry, and dark place in a mesh bag or paper bag, keeping a vigilant eye out for mold.

In the fall, these bulbs can be planted in your garden. Pay attention to required planting depths. Bulbs cultured in soil generally fare better than those in forcing jars or gravel, but within one, two, or more seasons, your bulbs will return to full bloom in their new, natural outdoor environment.

Copyright 2011, Joseph M. Keyser