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Forcing Bulbs

January 08, 2014

If winter is that season that seems to drag on for you, try forcing bulbs to bring in the smells and colors of spring right inside your home. This is a fun project to experiment with if you have the time and space.

All spring bulbs require a chilling period before they’ll bloom.  This includes tulips, daffodils, hyacinths, crocus, Dutch iris and scilla. Cool temperatures stimulate the biochemical response inside the bulb that “turns on” the embryonic flower so it will begin developing. Most bulbs require anywhere from 6 to 18 weeks of cold before the flower is fully formed. At that point they’re ready for light and heat. If you cut the cooling time short, the flowers may still emerge, but they might be stunted and deformed.  It is important to know what bulbs you have to determine the proper chill time.

For indoor blooms, the easiest bulbs are crocus, hyacinth, muscari, and mini-daffodils. Tulips and standard daffodils can also be forced, but they require a little more care and attention.

Bulbs look best in a shallow, wide pot that’s 4 to 6 inches deep. There should be at least 2 inches below the bulbs for root growth. The very top of the bulbs can be even with the pot rim. Use a standard potting mix (2/3 soilless mix, 1/3 compost/soil). Potted bulbs also look best when they’re crowded, so plant the bulbs together about 1/2-inch apart. It’s also good to stick with one variety of bulb per pot, because cooling and bloom times vary. Water thoroughly after planting, and label each of your pots with variety name and planting date. This will help you to remember what’s what and how long they have chilling.

Finding the right place to chill your bulbs is usually the biggest challenge. Once planted, the bulbs need to be kept at 40 to 48 degrees F. for the entire cooling period of 6 to 18 weeks. The potted bulbs can be stored in an unheated basement, a ventilated crawlspace, cold frame, or even a refrigerator.

Once you remove your bulbs from cold storage, allow three or four weeks to bloom time. Wake the bulbs gradually, starting with about two weeks of indirect sunlight and 60 degree temperatures. When shoots are three to five inches high, move the pots to a 68-degree environment and a bright, sunny window. Once buds color, move the pot to indirect light again to prolong bloom.

After blooming, most people discard potted bulbs. If you find that impossible, keep watering the pots and start adding some fertilizer. When the foliage yellows (usually after a month or two), you can remove the bulbs and plant them outdoors. Just remember, it may be several years before the bulbs build up enough reserves to bloom again.

You will find that forcing bulbs is very fun and worth the time and space requirements. Once you have it mastered, you can begin to create and customize your presentations year after year.  It will definitely add some drama to your home in late winter.  Good luck and enjoy.  Spring will be here before you know it!

 By Nick Guthrie, Horticulturist at TBG



Chilling Time

The list below recommends the number of weeks of chilling required, followed by the number of weeks until bloom (in parentheses).

  • Tulipa (tulip), 6-20 (2-3)
  • Crocus, 15 (2)
  • Chionodoxa luciliae (glory-of-the-snow), 15 (2-3)
  • Galanthus nivalis (common snowdrop), 15 (2)
  • Hyacinth, 11-14 (2-3)
  • Muscari (grape hyacinth), 14-15 (2-3)
  • Narcissus (daffodil), 6-17 (2-3)
  • Scilla, 12-15 (2-3)

Source: The Netherlands Flower Bulb Information Center

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