Re: CULT: Heat Zone Map
From: GWhite & LRader <bentfork@navix.net>
Donald,
A heat zone map (and the only one I'm familiar with is the Am.
Horticultural Soc. plant Heat-Zone map) is somewhat opposite of the USDA Plant
Hardiness Zone Map. Whereas the USDA Hardiness Zone Map is an estimator of the
expected minimum temperatures encountered over the U.S., the AHS Heat Zone Map
is an estimator of the number of days with temps over 86 degrees F that may be
encountered over the U.S. As you mentioned, very hot days and nights over an
extended period is very stressful to plants and may be more of a problem than
cold temps. The Heat Zone map is based on 12 zones across the U.S. and goes
from zone 1 (<1 day over 86F - ie most of Alaska and very high mountainous
areas) to zone 12 (>210 days over 86F -ie pockets in extreme southern Texas
and Florida). You mentioned that you are in Hardiness Zone 7, which
translates to an expected minimum temperature of 0 to 10 degrees F. While both
north-central Texas and parts of Tennessee are both in Hardiness Zone 7, these
two areas are in very different Heat Zones. Most of east Tennessee is in Heat
Zone 7 (60 to 90 days with temps over 86F) whereas central Texas (Abilene, for
ex.) is in Heat Zone 9 (120 to 150 days with temps over 86F). This difference
can be even more dramatic. The mountains of western North Carolina are in
Hardiness Zone 6 (min temp of 0 to -10F) but in Heat Zone 4 (only 14 to 30 days
over 86 degrees F). Amarillo, TX is also in Hardiness Zone 6 but is in Heat
Zone 8 (90 to 120 days with temps over 86F). So, whether you live in Amarillo,
TX or Asheville, NC, you are in Hardiness Zone 6 but the plants you grow are
much more affected by heat in Amarillo than in Asheville. Of course there are
many other climatic differences here too (such as rainfall, etc), but you still
must grow plants that are much more heat tolerant if you are in Amarillo than
if you reside in Asheville.
The down side of the Heat Zone Map is that it is not yet widely used except
by the American Horticultural Society. Most issues of The American Gardener
magazine have a Plant Heat-Zone Map near the back of the publication and lists
both USDA Hardiness Zone and AHS Heat Zone ranges for plants discussed in the
issue. Also, you can purchase a 2 x 3ft poster of the AHS Heat Zone Map. For
more info, call (800) 777-7931 ext 45. The price of this map is not listed in
the magazine. At any rate, I think that the combination of the USDA Hardiness
Zone Map and the AHS Heat Zone Map should really help pinpoint whether a
particular plant will do well in your area or not. Iris cristata, for
instance, is listed as hardy in USDA Hardiness Zones 3-8 and in AHS Heat Zones
8-1. Using this info, Iris cristata could be expected to live in Asheville, NC
(Hardiness Zone 6, Heat Zone 4) but not in Abilene, TX (Hardiness Zone 7, Heat
Zone 9) all other things being favorable, of course.
I hope this rambling note helps explain the Heat Zone Map. The addition of
the Heat Zone Map makes a lot of sense to me in that it helps explain why I
have more difficulty growing certain plants here in southeast Nebraska than I
did in northern West Virginia. Both areas are in similar hardiness zones, but
there are many more hot days in Lincoln, NE than in Morgantown, WV, hence the
different Heat zones (7 in Lincoln, 5 in Morgantown). I spend much more time
here in Nebraska trying to keep siberian and japanese irises thriving than I
had to expend in West Virginia. And most of that extra care is due because of
the summer heat difference, I believe. On the other hand, bearded irises
thrive here with less attention than in WV.
Gary White
Lincoln, NE (Hardiness Zone 5a, Heat Zone 7)
By the way, did anyone notice the iris on the cover of the May/June issue of
The American Gardener magazine? It is a very nice photo of MYSTERIOUS MONIQUE,
which they say is a cultivar of Iris virginica. I thought that MYSTERIOUS
MONIQUE is a cultivar of Iris versicolor. My specimen of Mysterious Monique
is blooming very nicely in my garden as we talk and I have it labeled as a
cultivar of I. versicolor. So, who is correct here? I. versicolor
(Hardiness Zone 3-8, Heat Zone 9-1) and I. virginica (Hardiness Zone 4-9, Heat
Zone 9-6). This would indicate that I. virginica should only grow in warmer
areas of I. versicolor's range, but I purchased my Mysterious Monique from
Joe-Pye Weeds Garden in Massachusetts (Hardiness Zone 5, Heat Zone 4) which is
more evidence that MM is I. versicolor, not I. virginica.
Donald Eaves wrote:
> From: "Donald Eaves" <donald@eastland.net>
>
> Gary White writes:
>
> > Southeast Nebraska is in USDA Hardiness Zone 5a, but in
> > American Horticultural Society plant Heat-Zone 7. Heat Zone 7 means that
> there
> > are 60-90 days per year in which the temperature is 86 degrees F (30
> degrees C) or
> > higher. I think that the extra protection from the sun that these plants
> get in
> > the afternoons, as well as slightly cooler temperatures, and more
> moisture
> > retention is very important during these hot, dry periods in the summer.
> From Donald Eaves:
> I certainly agree with the importance of temperatures, but am not familiar
> with
> any classified Heat-Zones. Can you tell us more? I think Linda Mann is in
> Zone
> 7 Tenn., as I am in Texas but I suspect there is a huge difference in our
> growing
> conditions. I personally always suspect warm and sometimes hot night temps
> over an extended period of time kill more plants than the cold temps during
> the
> winter.
>
> Donald Eaves
> donald@eastland.net
> Texas Zone
>
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