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Plan Now For Winter Blooms

Posted: October 1, 2013

Garden centers are currently stocking hardy bulbs, tantalizing gardeners with the prospect of spring color and fragrance. However, with a little advance planning and some knowledge of indoor forcing, it is possible to enjoy a patch of spring beauty even when midwinter is at its bleakest.

Indoor forcing is the technique by which spring bulbs can be tricked into breaking dormancy and blooming indoors. After a period of cold storage, bulbs can be grown in soil, in a pebble filled bowl, or simply grown in water in a specially shaped bulb vase.

Paperwhite narcissus is an excellent choice for forcing, since it requires no chilling in order to bloom indoors. Paperwhites are commonly nestled into a bed of pebbles or marble chips in a shallow waterproof bowl, or in a tall clear cylindrical vase. The latter will minimize the floppiness of this vigorous grower, as well as give a peak at its sinuous white roots. Firm the bulbs into the pebbles deep enough to support them upright, adding more pebbles if necessary. For best results, space the bulbs closely, but not touching each other. Finally, fill with water just to the base of the bulbs—any further may encourage them to rot. Provided the water is kept at a proper level, the bulbs should bloom in three to five weeks.

The most common variety of paperwhite narcissus to be found in nurseries is Ziva, which boasts clusters of pure white flowers and a heady, intoxicating aroma. If you belong to the vocal minority which finds Ziva's scent too strong, try Inbal or Ariel instead. Both have a softer fragrance and equally radiant flowers. Be prepared to search, however, as these are less readily available than Ziva.

All other bulbs will require a period of cold storage at 35-48 degrees in order to put on their best indoor performance. Bulbs may be chilled in any cold dry location such as an unheated garage or crawlspace where temperatures hover around forty degrees. If storing bulbs in the refrigerator, don't store in the same cooler as fruits or vegetables. These give off ethylene gas which can be harmful to the embryonic flower inside each bulb. As some bulbs are poisonous, don't store bulbs in the refrigerator at all if you have small children.

Another candidate for water forcing is the hyacinth, which for best results will require a period of cold storage for 10-14 weeks. After the period of chilling, hyacinths may be rooted in pebbles or in a specially shaped glass bulb vase, which has a pinched neck to support the bulb just above the water level. Excellent varieties for forcing include Pink Pearl, the rich blue Peter Stuyvesant and pure white Jan Bos. Don't be discouraged if you cannot find a particular variety at your local garden center. Most bulb displays will identify the varieties most suitable for indoor forcing.

Tulips and daffodils are somewhat more challenging, as they require a longer forcing period and are best potted in soil. For best results, turn to the smaller varieties, such as Kaufmanniana and Greigii species tulips, and dwarf tête-à-tête daffodils. Use a container with good drainage, and plant the bulbs densely, nose end up and slightly exposed. Plant tulip bulbs with the flat side facing outwards so that the largest leaves will face the outside of the cluster. Tulips will require a chilling period of 14 to 16 weeks, and daffodils a chilling period of 12 to 14 weeks.

Also quite lovely are the minor bulbs, such as crocus, snowdrop, grape hyacinth, and reticulated iris. These are especially effective when potted up in dense groups, though crocus can also be rooted individually in tiny bulb vases. All will require a chilling period of about 15 weeks.

Any forced bulb will benefit from being gradually introduced to warmer temperatures and increasing light. Once in bloom, they will last longer in cooler temperatures. Many gardeners choose to plant several batches, and introduce them gradually through the winter for maximum display.

Forcing depletes the bulbs' energy reserves, and many gardeners simply discard bulbs after forcing. If planted outdoors, a forced bulb may regain its vigor in a few years.

Contact Information

Kate DeSimone
  • Penn State Master Gardener