23 March 2009

Discussion in 'Vancouver Cherry Blog' started by Douglas Justice, Mar 23, 2009.

  1. Douglas Justice

    Douglas Justice Active Member UBC Botanical Garden Forums Administrator Forums Moderator VCBF Cherry Scout Maple Society 10 Years

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    The city should be awash in cherry blossoms. At the vernal equinox last year, ‘Jugatsu-zakura’, ‘Autumnalis Rosea’, ‘Whitcomb’, ‘Accolade’, and ‘Okame’ were all blooming. Of course, the trouble has been the roller coaster weather. It doesn’t feel like it’s been particularly warm since November, does it? Every time the mercury started to edge upward, another “cold low†showed up and put pay to our Lotusland reputation (did anyone else notice that it was 12 C in Toronto last week?). Face it, the weather here is unpredictable. I’m usually fond of saying that February is a good month to spend somewhere else, but really, it was pretty dry and bright and only as cold as you’d expect for February. But what happened to March (and November, December and January)? This year, even the purple plums (Prunus cerasifera) are barely showing colour. News flash! I see that late today we had a couple of postings: ‘Okame’ and ‘Whitcomb’. The ‘Okame’ are near Nitobe Garden at UBC and are really just starting to open. Last week I was startled to see a number of ‘Whitcomb’ revving up to full throttle in the parking lot at the north end of Oak Park. All is evidently not lost.

    Most hardy trees need a minimum exposure below a certain temperature before being physiologically ready to resume growth in the spring. This is built-in protection—evolutionary insurance, if you will—so that the tree doesn’t start growing when freezing temperatures are still a probability. And it’s why some fruit trees can’t be grown in California: because it doesn’t get cold enough to satisfy their requirement to end flower bud dormancy. With respect to cherries, most don’t need that much winter cold before they’re able to break dormancy in the spring. Once that chilling requirement is met, they require a minimum exposure above a certain temperature before they buds will start to expand, and then, some won’t open at all unless the temperature is downright warm. Again, it’s all about insurance. As a Vancouverite, I consider 8 C to be balmy (it’s warm enough to wear sandals, for heaven’s sake). Cleary, ‘Okame’ and ‘Whitcomb’ are with me on this. The point is that different cherries have different temperature requirements for breaking dormancy, for bud expansion and for opening. The ‘Autumnalis’ types clearly have very little chilling requirement, blooming as they will in October, but they also don’t have a big heat requirement for bud expansion and opening, either. All of those flowers got frosted this year.

    I’m sorry to say that most of this sort of research has only been worked out in principle and the temperature requirements for specific cherries is not well known. Such unpredictability makes for nervous event planners. Will the cherries be in bloom when I lead my tour? Good question. I have to admit that this unpredictability appeals to me on an existential level. Sometimes it’s just better to accept what comes. It’s not like we can affect it, anyway. Enjoy the snow next week.
     

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