I was Christmas shopping at a local garden store and found a bin of tulip bulbs marked down for sale, with instructions for "forcing" them for winter color. Brought them home, and then read the instructions:
"Water well and place in a cool spot (35-50F) for 14-15 weeks. Move to a cool, dark spot for 1 week and then bring into full sun for flowering."I have enjoyed amaryllis and paperwhites in previous winters, but these instructions puzzle me. I quite understand that bulbs accustomed to four-season temperate climates need to be "stratified" with a period of cold to "fool" them into thinking winter is over and it's ok to grow.
But 14-15 weeks?? Plus one more? Four months from now will be the end of April, when I'll be out planting in the garden for real. There is no winter bloom to enjoy in the interim.
And for that matter - as a general question about stratifying - how does a bulb "know" how long it has been chilled? Is there some kind of molecular clock in the cells that has to spin at a lower rate for a longer time to trigger the cell division of spring? If a bulb is totally dormant in my flower bed when outside temps are 20 below zero, how could it ever know whether it was dormant for 3 months or for 3 days? I know plants can be fooled out of dormancy by spring thaws, but why can't I just chill my tulip bulbs for 3 days and then warm them up?
Addendum: A likely answer to my question, courtesy of reader Vireya:
It may be something like the chilling time for fruit trees, which produce a dormancy hormone that gradually breaks down while the temperature is between freezing and 7C (sorry WilliamRocket). When the hormone is completely broken down the buds can swell and burst. That takes different numbers of hundreds of hours for different varieties.
This journal article suggests that the tulip chilling requirement is also hormone related, although it says that "The mechanism of sensing the low temperature period is unknown". But it is 19 years old, so maybe there is more info out there somewhere now?
a quick googling says that chilling tulips for 14 to 16 weeks is about right. here is one of many urls, this one with a short chill guide at the end: https://www.whiteflowerfarm.com/blog/index.php/2017/11/21/forcing-bulbs-its-easier-than-you-think/
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Right. But how does a garden center sell bulbs at the end of December "for winter color" if they are to start growing at the end of April?
DeleteAm I supposed to appreciate the winter color of the bulbs?
I'm guessing that they originally offered these in about September and are now doing an end-of-year clearance of the ones that didn't sell back then.
Deletemy thinking as well.
Deletea smart GC would have chilled the bulbs starting in september, and put them out for sale now. one is probably not thinking in september: 'oh, i have to chill some bulbs now, so i can enjoy them in january'. that thought occurs in the midst of the doldrums of january, when one thinks: 'i need to see color, and smell fresh growth!'.
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p.s. if your tulip bulbs are already sprouting, then they may have already had enough chill time? maybe plant them, so they can root, and keep them chilled them for a week or two, and them bring out into the warmth and sun?
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I can't answer all your questions, but I know that here in New Zealand where we use the metric system, any bulbs in the ground when it's 20 below zero never sprout.
ReplyDeleteSometimes I think back to pre 1987 days when we still used the old fashioned temperature scale and I am sure there were far more flowers then.
Damn you, Celsius, damn you and all that scale with you.
How they know how much cold they've had is an interesting question. It may be something like the chilling time for fruit trees, which produce a dormancy hormone that gradually breaks down while the temperature is between freezing and 7C (sorry WilliamRocket). When the hormone is completely broken down the buds can swell and burst. That takes different numbers of hundreds of hours for different varieties.
ReplyDeleteThis journal article: https://academic.oup.com/jxb/article/51/344/587/623239
suggests that the tulip chilling requirement is also hormone related, although it says that "The mechanism of sensing the low temperature period is unknown". But it is 19 years old, so maybe there is more info out there somewhere now?
Thank you. That would make sense. I've added your information to the post. :-)
Deletei cannot remember the name of the book, nor the author, but the book was a compendium of thousands of seeds and bulbs, listing their dormancy periods, germination times, etc. these were all done by the author. the last time i heard / saw one was in the early 1990s.
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