16 December 2010

Coaxing bulbs for an early spring

Coaxing bulbs to bloom indoors before spring is called forcing. The leafless, winter-dormant bulbs are chilled and then gradually warmed indoors to convince them to send up leaves and flowers.

Some bulbs are given a cold period (35 to 55 degrees) outside, in a cold garage or refrigerator and then brought inside to a warm, sunny location where they bloom.

Warm-climate Paper white narcissus (Narcissus tazetta), Soleil d’Or, Chinese sacred lily (N. tazetta var. orientalis), and Amaryllis (Hippeastrum) can be grown inside without a chilling period.

Plant vendors, such as Southwood Nursery (9025 S Lewis, Tulsa) sell pre-chilled bulbs. Select the largest bulbs you can find since they have the most food available to produce flowers.
At this time of year, pre-chilled bulbs are identified as good for forcing.

Other bulbs that are often forced for indoors flowers include tulips, hyacinths, grape hyacinths, crocus, snowdrops, scilla, muscari, and anemones.

Paper whites, hyacinth and crocus can be grown in pebbles and water in the bottom of a bowl or tall vase. All the other spring bulbs are grown in soil filled containers with good drainage. Pots, planter boxes, old cream pitchers, retired bread trays, hypertoufe containers and other unique and artistic containers can be used.


Do not use garden or bagged potting soil mix. A homemade mix of sand, soil, spaghnum moss, plus either perlite or vermiculite is best. Any bagged “soil-less” mix can be used.

Add some low nitrogen fertilizer such as bulb food or 5-10-5 to the mix. Or add water soluble houseplant food at half-strength when moistening the mix.


Fill containers three-fourths full with moistened planting mix. Set bulbs close together. Tulips are planted with the flat side to the outer edge of the pot. When bulbs are in place, fill in with planting mix, leaving the tip of the bulb exposed. Water and add more soil if it settles down below the growing tip. The entire bulb should be below the rim of the container.

To create the cold, dark period, put the pots in a cold place and cover loosely with newspaper, paper bags or plastic. If you chill the bulbs in a refrigerator, they will have to be checked more often for water since the condenser will dry them out faster.

Bert Leek at Touch of Nature (www.touchofnature.com and 770-237-0993) said that in the nursery business, tulips get 6-weeks in a cooler and then 4-weeks in a chilly, rooting room. He said home gardeners can let Mother Nature do the work.

Plant the tulip bulbs in 6 or 8 inch deep pots and put the pots outside, then surround and cover with mulch such as leaves and straw, Leek said. In 8 weeks, begin to check them for growth. When they have 2-inch tall green sprouts, bring them inside to bloom.

Chilling times: Crocus, daffodil, Glory of the Snow (Chiondoxa), Grape Hyacinth, Iris danfordiae, and Tulip prefer 15weeks. Hyacinth 11 weeks.

Tropical bulbs have never had a cold winter so they need no pre-chilling to bloom.


The bulbs will begin to grow roots and in a couple of months roots may even emerge from the container’s drain hole.

When the bulbs have chilled for the required time, bring them inside and put them in a cool place. Bright light is not necessary. When green starts to show, move the pots to a warmer, brighter location for a few days. You are trying to mimic spring with gradually warmer temperatures and slightly longer hours of light. A sudden transition can cause a blast of the bud and failure to flower.

The bulbs will bloom within a few weeks. Move them out of direct sun. To have flowers for several weeks, bring in a pot every week or two.

There will be photos of the process on my blog tomorrow and there is more information at http://tinyurl.com/28bugqm.

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