We live in a strange zone: Sunset 17, USDA 9 and it's been a little difficult to figure out whether I'm a fool for trying a tree that requires 600 or 700 hours of chill. We're on the California central coast, but temperatures at night can range from mid 40s at the beach to below freezing 5 miles inland. So it's not just a matter of consulting the local weather station numbers.
So, I put a "weather system" out in our backyard. Is it merely a matter of averaging out the temperatures between the 3 thermometers and counting up the number of hours under 45 degrees F to know whether my yard will supply sufficient chill?
Should I discount any chill hours that happen after the trees have blossomed, which sometimes happens in early Feb?
Also, any recommendations for a formula that subtracts chilling hours if the day time temperatures go over 60, which they often do here in Dec and Jan.
Thanks.
We've found figuring chilling hours is an inexact science and we've seen all kinds of models, with each having their own problems. Some of it depends on the fruit you're trying.
Apples are quite forgiving and will fruit in just about any zone; we grow them fine with under 400 hours, even ones rated 1000 hours. But stonefruit like peaches and apricots are pretty rigid, and you may end up with a shade tree if you don't pick the right varieties.
But there is no need to sacrifice, as there are plenty of top-quality low-chill stonefruit to pick from with successive ripening dates. Tom's Picks is a good place to start.
http://www.davewilson.com/homegrown/all ... Picks.html
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