This is a public-interest archive. Personal data is pseudonymized and retained under GDPR Article 89.

Zones (lengthy)

Square Foot Gardening List - http://www.flinet.com/~gallus/sqft.html

Several weeks ago, I was asked to help clarify the "zone confusion"  in
response to questions on our arid_gardener email  list   Hope this
clarifies and does not add to the confusion.  Summary of my research
follows:

"There is a world of difference between USDA zone 9, Sunset zone 9, and
Heat-Zone 9. The USDA zones only indicate the cold hardiness which
doesn't indicate if the plant is adapted otherwise. The AHS Heat-Zones
only
indicate the plant's tolerance to heat. None of the zones take into
account environmental factors such as stress due to pollution, security
lighting an toxic wastes; increased plant vigor due to improved
management systems; or stresses due to planting in artificial
environments (malls, freeways, next to buildings). The zone ratings are
not perfect but are a good place to begin. To review my understanding of
the zone ratings:

USDA PLANT HARDINESS ZONES

The current map of the USDA Plant Hardiness Zones is the 1990 version
which is based on the average of the lowest temperatures recorded for
each of the years 1974 to 1986. The map shows 11 zones: Zone 1
represents temperature lows below -50 degrees F, zone 11 represents
lows above +40 degrees F (essentially frost-free). Zones 2 through 10
are each divided into 10 degree zones, then further divided into two 5
degree sub zones, designated "a" and "b", but plant listings don't use
the sub zones.   The best map I have
found on the web is at the National Arboretum at
http://www.ars-grin.gov/ars/Beltsville/na/hardzone/hzm-sw1.htm .
There is also a zone finder at the Time-Life Virtual Garden at
http://www.vg.com/cgi-bin/v2/gemag/PID=69909416995854636609308,09308&s=4
536
which requires you the enter your postal zip code, then returns your
zone number.  The land grant universities in some states
(e.g., FL and TX) have web sites with maps showing county boundaries
which are overlaid with the plant hardiness map showing the zone
boundaries within the counties. This improves the resolution.  Most
eastern gardeners find the USDA zone designations useful but they are
less useful in the southwest where geographic, climatic and physical
influences affect plant adaptability more than does cold hardiness.
Following is a list of the low temperature ranges for each zone and sub
zone:

USDA Zone Temperature Range
======= ==========
1 Below -50 F
2a -50 to -45 F
2b -45 to -40 F
3a -40 to -35 F
3b -35 to -30 F
4a -30 to -25 F
4b -25 to -20 F
5a -20 to -15 F
5b -15 to -10 F
6a -10 to -5 F
6b -5 to 0 F
7a 0 to 5 F
7b 5 to 10 F
8a 10 to 15 F
8b 15 to 20 F
9a 20 to 25 F
9b 25 to 30 F
10a 30 to 35 F
10b 35 to 40 F
11 above 40 F


SUNSET ZONES

The Sunset zones, established by Sunset Books, are the most useful for
the Western states but lass so for the Eastern US.  The zones consider
winter lows, summer highs, length of growing season, humidity, rainfall
patterns, latitude, elevation, continental air influence, and local
terrain. The zones assigned to the plant listings in the Plant
Encyclopedia of the Sunset Western Garden book Sunset National Gardening
book and are a pretty reliable indication of the plant's adaptation. One
limitation is it only lists plants in common use at the time of the
book's latest printing (1995 for the Western book) and the numerous
subsequent plant introductions are not listed.  And you also need to buy
Sunset's book(s).  To find your Sunset zone, go to url
 http://sunsetmag.com/Reference/GardenRef/ZoneFinder.html
and fill in the from.

AHS HEAT ZONES

The American Horticultural Society has developed a USA Plant Heat-Zone
Map that assigns geographical zones of plant tolerance to heat. The AHS
plant heat-zones complement USDA plant cold-hardiness zones and Sunset
climatic zones as an additional aid in plant selection for a given
region. As gardeners know, not all plants that are cold-hardy in USDA
zone 9 (Phoenix AZ) can withstand our intense summer heat; it follows
that not all plants that are heat-tolerant in the new AHS heat-zone will
also withstand the coldest days in USDA zone 9. The map defines 12
color-coded zones based on the number of heat-days occurring annually in
each zone. A heat-day occurs when the temperature exceeds 86 degrees F.
The temperature 86 degrees F was chosen because (according to AHS) plant
cellular proteins are damaged - a few years of observation in the
Phoenix AZ area suggests this breakdown occurs at a higher temperature
because many of our desert plants seem to prosper well into the 90s. The
temperatures used to establish the heat-zones are the 22-year
statistical averages recorded from 1974 through 1995. You can
download the map from
http://www.suite101.com/userfiles/79/hz1024.jpg  ,
buy it from AHS or buy the book (see www.ahs.org for links). The book,
"Heat-Zone Gardening" contains a picture gallery, with the temperature
profiles, of 460 landscape plants and herbs.  The profiles list only the
genus and does not provide any details for plants with temperature
tolerances that are species dependent.  Possibly the best use of the
heat-zone ratings is to help identify plants that are marginally
adapted.

Olin, near Phoenix AZ
USDA Zone 9b
Sunset Zone 13
AHS Heat-Zone 11
_______________________________________________
Arid_gardener mailing list
Arid_gardener@Ag.Arizona.Edu
http://Ag.Arizona.Edu/mailman/listinfo/arid_gardener
Archives - <http://Ag.Arizona.Edu/pipermail/arid_gardener/>


______________________________________________________________________
To unsubscribe, write to sqft-unsubscribe@listbot.com
______________________________________________________________________
Applying to college this year?
Apply online at Embark.com and enter the Embark.com Tuition Sweepstakes! You could win $80,000 for tuition to the college of your dreams! Enter daily to increase your chances of winning: Sweepstakes ends 1/15/00. Click to enter: http://www.listbot.com/links/embark
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index