[NAFEX] USDA Zones chill hours & heat etc - Sunset Zones

Stephen Sadler Docshiva at Docshiva.org
Sun Dec 11 15:34:45 EST 2011

You are absolutely right. USDA zones or other single factors do not imply
that a plant that thrives in one place will survive another.

An extremely useful tool, which I wouldn't mind at all if this group
adopted, is the Sunset Climate Zones Map:


It combines all those things you wrote about. 

Sacramento, Sunset 14 
moving to Charlotte, Sunset 32

ZONE 14: Northern California's inland areas with some ocean influence
Marine air moderates parts of Zone 14 that otherwise would be colder in
winter and hotter in summer. The opening in Northern California's Coast
Ranges created by San Francisco and San Pablo bays allows marine air to
spill much farther inland. The same thing happens, but the penetration is
not as deep, in the Salinas Valley. Zone 14 includes the cold-winter valley
floors, canyons, and land troughs in the Coast Ranges from Santa Barbara
County to Humboldt County. The milder-winter, marine-influenced areas in
Zone 14 and the cold-winter inland valley within Zone 14 differ in humidity.
For example, lowland parts of Contra Coasta County are more humid than
Sacramento. Fruits that need winter chill do well here, as do shrubs needing
summer heat (oleander, gardenia). Over a 20-year period, this area had lows
ranging from 26 to 16º F (–3 to –9ºC). Weather records show all-time lows
from 20 down to 11ºF (–7 to –12º C).

ZONE 32. Interior Plains of Mid-Atlantic States; Chesapeake Bay,
Southeastern Pennsylvania, Southern New Jersey
Growing season: late Mar. to early Nov. Rain falls year-round (40" to 50"
annually); winter lows (moving through the zone from south to north) are 30
degrees to 20 degrees F/-1 degree to -7 degrees C. Humidity is less
oppressive here than in Zone 31.

We also have a home in Sunset 1A. The plant variety is much more limited
than the USDA zone would imply.
Zone 1A: Coldest mountain and intermountain areas of the contiguous states
and Southwestern British Columbia
Marked by a short growing season and relatively mild summer temperatures,
Zone 1A includes the coldest regions west of the Rockies, excluding Alaska,
and a few patches of cold country east of the Great Divide. The mild days
and chilly nights during the growing season extend the bloom of summer
perennials like columbines and Shasta daisies. If your garden gets reliable
snow cover (which insulates plants), you’ll be able to grow perennials
listed for some of the milder zones. In years when snow comes late or leaves
early, protect plants with a 5- or 6-inch layer of organic mulch. Along with
hardy evergreen conifers, tough deciduous trees and shrubs form the garden’s
backbone. Gardeners can plant warm-season vegetables as long as they are
short-season varieties. To further assure success, grow vegetables from
seedlings you start yourself or buy from a nursery or garden center. Winter
lows average in the 0 to 11°F (–18 to –12°C) range; extremes range from –25
to –50°F (–32 to –46°C). The growing season is 50 to 100 days.

-----Original Message-----
From: nafex-bounces at lists.ibiblio.org
[mailto:nafex-bounces at lists.ibiblio.org] On Behalf Of Martha Davis
Sent: Sunday, December 11, 2011 11:02 AM
To: nafex at lists.ibiblio.org
Subject: Re: [NAFEX] USDA Zones chill hours & heat etc

Hi all,

I hope I don't sound like I'm ranting too much.  Mostly I'm trying to
facilitate clear communication.

Minimum temperatures, which is the USDA zone basis, are different from
chill hours, and both are different than amount of summer heat (growing
degree days) which is different than summer maximums.  In some parts of the
country (I think low elevation midwest and east) they all move together,
but not in others, typically a lot of the west.  For some fruits it appears
that strong sun can substitute for summer heat, but probably not always. I
live where my average minimum temp is somewhere in the 0 to -10 range right
on the edge of zone 5/6, that really only says something about cold
hardiness, nothing about how much chill hours I want or get or how much
heat. I want trees with a high chill requirement (hours between 32-45 F)
ideally around a thousand because we get erratic winter warmups and it is
easy to satisfy low chill requirements with a week of weather in 35-70 F
temp range in February before it drops down to the teens & lower and then
bounces up enough to start bloom and down some more.  Even though I am at
the border of 5/6, because we cool into the 50ties on a lot of summer
nights I still don't get enough heating degree day units to grow most
tomatoes well, which has implications for many fruit crops. If you can
distinguish between all these things in your experience or your reference
it is helpful to be more specific. It may also help when you move to a new
climate area especially without experienced people around.  There are
reasonable chill hour maps on line, and some heat zone maps (based on
summer maxs) the degree day ones are harder to find because they are often
crop specific.  Just knowing whether it cools off much on summer nights is
useful.  Min max thermometers are always good, it can be very educational
to look at your minimums for summer nights depending on where you are.
 Just looking at USDA Zones and American Horticultural Society heat zones
Chicago looks a lot like high elevation NM. The winter mins and summer maxs
are fairly similar.  When you look at variation in winter temps, desirable
chill hours and growing degree days, or even just summer minimums they are
different worlds and the plants know it.  It has been a real education
moving here.  I look to Maine and western Oregon to get variety ideas
regarding tolerance for low growing degree days, IL for season length, and
winter minimums, and experimenting for a lot of other things.

Martha  Davis
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