Bay area Tulipa

Paul Licht
Thu, 11 Apr 2013 14:27:46 PDT
Your comment on the importance of microclimate variation is 
obviously relevant. However, the chilling data you refer 
seems to lack too important elements for us: they refer to 
air, not ground temperature and they do not address how much 
chilling each bulb species requires.

Paul Licht, Director
University of California Botanical Garden
200 Centennial Drive
Berkeley, CA 94720

On 4/11/2013 1:49 PM, Nathan Lange wrote:
> For people living in California, the University of California
> provides chilling accumulation models with data for many locations
> throughout California:
> This information is provided for fruit and nut growers but is very
> useful for growers of other species requiring vernalization and/or
> stratification.  Other universities likely provide similar
> information.  This data is mostly limited by the number of
> locations.  The amount of winter chilling varies greatly in the Bay
> Area between years and especially by location.  For example, If you
> look at the data for the "Oakland Foothills" which is the closest
> station in Alameda County most similar to the University of
> California Botanical Garden, there have only been about 450 to 900
> cumulative chilling hours per year since 2004.  However, if you live
> 30 miles away in Pleasanton (further inland), there have been about
> 800 to 1200 cumulative chilling hours per year since 2004.  With such
> huge annual chilling differences, successful flowering of many
> species requiring "more" vernalization will undoubtedly vary
> significantly from year to year in marginally cold locations like Berkeley.
>   From a cumulative chilling perspective, this past winter has been
> one of the coldest in the Bay Area in years.  So far, I have seen
> this reflected in both earlier, more uniform flowering times for
> bulbs that generally require more vernalization (Tulips) and
> outstanding germination rates for species (Calochortus, Fritillaria)
> planted late.
> Nathan
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