I just found a resource produced by the California Energy Commission
that "lists the climate zones associated with several thousand
It lists my zone as Zone 12, while the Western Garden Book lists my
zone as Zone 9. Who am I to believe?
(Zone 9, no, make that 12, no...)
You are to believe your plants (or look at what your neighbors are growing
or what the local nursery sells). California has so many micro climates
that there is no fast safe rule. If you are by the ocean your temperatures
are going to vary far less than if you are inland. If you are going up into
the mountains you have to consider latitude, what side of the hill you're
on, wind patterns and all kinds of things. Are you in a protected valley or
a valley where the cold settles is yet another varient in that area.... My
Mother moved from San Bernardino which as a 9 zone rating and where we had a
thriving bougainvilla to Escondido with zone 11 where for the life of her
she could not get a bougainvilla to survive (but all of her hawaiian type
If it were me I would assume a zone 11 and try plants with that zone range
that are not expensive and then move in the appropriate direction of zone
from how the plants do.
BTW, the zone 9 chart was re-evaluated this year and its changed again.
I don't think it has been released yet. (like the flood plain re-eval we
are supposed to get this year due to Tropical Storm Allison 2 years ago)
Somewheres north of the tropic of cancer.
J. Kolenovsky, A+, Network +, MCP
=F4=BF=F4 - http://www.celestialhabitats.com - business
Do you mean the Sunset Western Garden Book? If so, they use their own
proprietary zone system with 24 zones. The site in your url appears to
use it's own proprietary zone system as well. In fact, it doesn't look
like a "zone" map as much as it looks like a district map with no
duplicate numbers (except for 14 and 15 being split in two each).
Most of the time when people talk about zones without prefacing it with
a proprietary name they're referring to USDA zones. That system uses
nine zones numbered 2-10 Check your USDA zone here:
Or enter a zip code here:
The USDA zones only represent average low temperature in winter. I
believe that the Sunset system takes into account average summer highs
and humidity. The zones in your map are apparently based on energy use,
but do not represent any kind of range where 1 would be high or low, and
16 would be the other end. They appear to be numbered consecutively in a
line on the coast, and then down and back up again inland.
Maybe Fleemo was referring to the California Energy Commission's 16
climate zones which, like Sunset's zones, are based on "temperature,
weather and other factors", but have no numerical coorelation to
Sunset's zones. Used primarily to predict and track electrical power
consumption for specific geographical areas. -Olin
You make a good point in that if a zone is referred to, the zone type
should be specified. The USDA Cold Hardiness zones are used to indicate
plant sensitivity to cold temperatures. The AHS Heat-Zones indicate
sensitivity to heat. The Sunset zones are true climatic zones and
include other relevant factors such as humidity, pH, temperature,
exposure, wind, elevation, coastal influences, etc. The Monrovia
Nursery has a brief comparison of the USDA, AHS, and Sunset zones with
links to the zone maps at
(The url may wrap)
The zone references are usually to the USDA zones. West of the
continental divide, the Sunset zones seem to be more useful.
Thanks for the info. It's a 5.7 MB File. Took just over 18 minutes to
download (48 KB/sec Modem).
From the description at
it looks like it will be too complex to use. I doubt that the current
zone designation will disappear soon. The AHS Heat-Zone ratings have
been out over five years and I have yet to see them used in catalogs or
on plants in a nursery. Plus there are several dozen plants in Dr.
Cathey's "Heat_Zone Gardening" book that are not rated for our Heat-Zone
(HZ 11 or 12 - kinda hard to tell from the maps) that grow very well
here (Phoenix AZ). Sunset's zones still seem to work best for us but
there are lots of new xeriscape plant introductions every year and it
seems to be difficult for Sunset to keep their Plant Encyclopedia up to
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