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Saturday, January 7, 2017

Forcing Tulips to Bloom on a Precise Date

Q. When should I put tulip bulbs in the fridge so that they bloom on Easter or a few days earlier. Can you please help me? I want a nice table centerpiece.

A. Getting tulips to bloom precisely at Easter is difficult for a homeowner because they frequently do not have enough information about the tulip or a precision growing environment. Commercial growers using greenhouses get plants to bloom precisely on a specific date by selecting known varieties and growing them at precise temperatures.

Some plants like mums and Christmas cactus, require controlling the length of darkness or the application of growth regulating chemicals at specific times. Tulips are a little easier. Most tulip varieties bloom in 4 weeks if the temperature is kept constant at 60F. Plants grow faster or slower depending on temperatures.

Plants grow faster in warm weather and slower in colder temperatures. If tulips are grown ten degrees warmer, 70F, subtract a week. If grown 10 degrees cooler, 50F, add a week. A few varieties may take 5 to 6 weeks to bloom at 60F.

For precision blooming, it’s best to know the variety of tulip being grown and how many weeks it takes to bloom. Some flowering plants require cold temperatures to bloom. We oftentimes have enough outside cold temperatures for tulips during winters in the Las Vegas Valley if they are planted on the north side of a building and in the shade. But it depends on the variety.

 To vernalize tulips (subjecting the bulbs to cold temperatures so they produce flowers) the bulbs are placed in a refrigerator 12 to 14 weeks. They will grow a little bit, slowly, at this temperature. Some varieties of tulip require fewer than 12 to 14 weeks. Some tulip bulbs are available pre-chilled.

 Here is how I would do yours.
  • Stick the bulbs in the refrigerator, upright, in slightly moist potting soil for 14 weeks. 
  • At the end of 14 weeks, put them at room temperature five weeks before you want them to bloom. If they are growing too fast, grow them colder; put them outside in the shade on the north side of the house to slow them down. When they are back on track, bring them back indoors. 
  • Water them when needed but don’t keep the bulb wet. The bulb can’t be dry either. It can lose roots that way. Use a soil moisture meter to judge when to add water. Fertilize lightly once a month with a water soluble fertilizer during warm temperatures. 
No guarantees it will be exactly on the date you want but it will be close.

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