West coast peonies
Lee Poulsen (Wed, 07 Jun 2006 13:49:00 PDT)

On Jun 7, 2006, at 12:12 PM, Max Withers wrote:

There are many different theories on chilling hours even besides the
two cutoff temperatures you mention (and some add negative chill for
hours above 65 deg. or 70 deg., or a 50% deduction per hour above some
upper cutoff).

Regardless of whatever theory you ascribe to, you guys up there in
(Sunset) Zone 17, and similar, have plenty. I believe that zone is the
only place in the entire U.S. where you can successfully fruit both
cherries and oranges every year--cherries requiring a lot of chill
hours (at least 900 and more typically 1000 or more each winter) while
simultaneously never dropping below about 25 deg. where you would lose
the oranges. The Calif. Central Valley also gets a high number of chill
hours, but only in very protected areas do they not risk losing their
orange crop frequently. It's much more marginal for them for oranges
and even more so for lemons than for you guys. Everywhere else in the
U.S. that gets 1000 hours of chill per winter is in USDA Zone 7 or
lower (except for some Zone 8 areas in the Pacific Northwest--but they
can't grow or fruit oranges up there).