Am I stressing over nothing?

Yup.

Whatever zone your house may be in (and few maps published in a
9x13-inch book can show areas down to that detail ;-) you seem to
be on or near a borderland. This means your temps are about
there, too. I'm not as familiar with the Sunset Zones as I used
to be, but being between zones 6-7 in the USDA scale shouldn't
require a heavily insulated greenhouse.

You can never get total accuracy, but strike an average between
the lows in each zone and you should be close enough. Then buy a
standby kerosene (or other) heater for those occasional Arctic
clippers that come rushing south out of Alaska.

Jim Lewis - - Tallahassee, FL - The phrase
'sustainable growth' is an oxymoron. - Stephen Viederman

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