Have held off, but am feeling so awful today that I think the USDA Hardiness Zone Map is gonna get it.
First of all, the Hardiness Zones only tell us what will survive the winter. Many people do not garden in the winter, so the Hardiness Zone plays little part in selecting veggies to grow. More to the point are data like length of growing season, dates of first/last average frost, annual precipitation, and so on.
A climate zone system, to be of practical use to gardeners, needs to account for these factors, as well as latitude, prevailing wind (makes a real diff. in humidity), elevation, etc. Which is why I always talk about the Sunset climate zone system
Although for some reason the USDA has assigned my zip code to a different zone than traditionally it's been assigned to (and I had to do a Captcha code
to get this precious nugget of information!
), my own experience gardening in this zip and in a zip 6 miles due south over the past two decades--the span of time the new map is based on--directly contravenes the winter minimum temperatures listed for my new zone.
The new zone says my winter minima are between 30 and 35 deg. F. Bullfeathers. Ha! My own memory, as well as newspaper stories, agricultural disasters, and other third-party sources, provide these proofs of different minima within the relevant 20-year time frame:
--late December; hard freeze (20-25 deg) for several consecutive days. Many well-established plants die throughout northern California; the Central Valley citrus crop is destroyed.
--A short hard freeze (25-28 deg); my normally outdoor cymbidiums, hardy down to 28 deg, are brought into the house for four days.
--January; even the snails stayed hidden wherever they hide, and there were a lot of killed rose canes to be cut off in the spring. Approx. 25 deg.
--January; more crop damage, and my jade plants suffered some damage. Approx. 25 deg., had to run supplemental electrical heater downstairs.
My Sunset zone hasn't changed at all: "In a 20-year period, the lowest winter temperatures in Zone 17 ranged from 36 to 23 deg F (12 to -5 deg C). The lowest temperatures on record range from 30 to 20 deg F (-1 to -7 deg C)" (Sunset Western Garden Book
, 2001 7th ed., p. 48).
And this is a comparison of the hallmark "hardiness" temps of my "new" USDA zone vs. those of my Sunset zone! Poor application of research; the USDA map strikes out, folks.
Sunset Zone 17, USDA Zone 9 (first, last, and always, it seems like