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Re: Re: temperatures and hardiness


> The AHS heat map is, IMO, completely useless.
Marge, do you suppose that might be why Cathey's $30 book is being sold off
for $3 by Hamilton books?
Kitty

----- Original Message ----- 
From: "Marge Talt" <mtalt@hort.net>
To: <gardenchat@hort.net>
Sent: Monday, April 12, 2004 6:15 PM
Subject: Re: [CHAT] Re: temperatures and hardiness


> Well, the USDA hardiness zones are just the tip of the iceberg.  They
> only deal with average low temperatures for given locations, not with
> all the other factors that determine a plants cold hardiness.  It's
> somewhere to start, but *only* a start.
>
> The AHS heat map is, IMO, completely useless.  As pointed out, it
> only shows the avg. number of days above 86F.  Whoopee!  Nothing at
> all about night temperatures nor humidity - two very important
> factors in whether a plant can survive.  Useless, useless, useless.
> Actually really annoys me that they published this and are making
> such a big deal of it (or trying to).  If it were really useful, that
> would be one thing, but it is not and as it stands it never will be -
> not to mention that only a minuscule number of plants have been rated
> according to that map.
>
> The USDA zones do help you figure out whether something has a prayer
> of surviving where you are because of cold.  If a plant is rated z9,
> someone in z4 needs to forget it in the open garden.  What I have
> learned is that most plants rated as hardy in z3 are not going to
> like summer in z7 - no matter whether the designation is z3-8 -
> having killed quite a few with that type of designation.  They might
> survive nicely in z 7-8 PNW but they ain't a gonna make it in the
> Mid-Atlantic or northern Alabama nor Texas.
>
> More to the point is where does the species plant originate?  What is
> its provenance?  If you know that, you can do a bit of research about
> the climate of that area and compare it to yours.  This is, still
> somewhat of a generalization because elevation makes a real
> difference; some plants from places you might think tropical just
> looking at a world map, come from very high elevations and are quite
> cold hardy - they might not be able to take hot, humid summer nights,
> but they survive cold winters.  Whether a plant comes from a winter
> dry or winter wet climate also makes a big difference - same with
> summer.  And, we must not forget our own garden micro-climates.
>
> Some plants are quite hardy in hot summer climates that are not in
> cooler summer climates (the UK, for instance) because they need a
> good long hot period to ripen.  Many plants you read about in English
> garden books say they need a warm wall to survive; given that where I
> am or where Pam is, they'd fry.  Many of our ornamental grasses are
> considered borderline hardy in the UK because it just doesn't get hot
> enough in summer for them....Miscanthus is one - bone hardy for me
> and in much of the US; hardly ever blooms in the UK.
>
> Some plants are quite hardy if given sufficient time to adjust to
> cold weather but will die fast when hot weather turns cold overnight.
>  Conversely, some plants are actually hardy, but tend to start
> growing at the first sign of warm weather in spring and get zapped by
> roller coaster spring frosts...think Hydrangea mac.  This has to do
> with how a plant develops its winter anti-freeze; some do it
> according to temperature and some according to day length; think some
> even combine these.
>
> Some plants are native and hardy throughout much of the US, but it
> makes a difference where they originated.  For instance, Cornus
> florida (dogwood) born and bred in the south will not be hardy in the
> north - even from seed.  So a "zone" designation for this plant,
> while interesting, does not tell you whether the plant in your hand
> (or your local nursery) is going to live through your winters.
>
> That said, you will never know whether you can grow a plant until
> you've tried and killed it at least 3 times, even one supposedly
> rated hardy where you are.
>
> </dismount zone soapbox>
>
> Marge Talt, zone 7 Maryland
> mtalt@hort.net
> Editor:  Gardening in Shade
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> ----------
> > From: james singer <jsinger@igc.org>
> > Sorry. Kitty got part A right. A-Z tries to fit plants into USDA
> [cold]
> > zones. And Noreen got part B right, A-Z's understanding of low
> > temperatures appears to assume a period of duration that does not
> > pertain, at least not in Zone 9 or above. It may or may not pertain
> in
> > lower zones, but I have no useful experience with them.
> >
> > On Monday, April 12, 2004, at 05:48 PM, ""
> > <gardenqueen@academicplanet.com> wrote:
> >
> > > You're right Cathy - the AHS heat zones are based on average
> number of
> > > days per year above 86 degrees. I've got the big map on my wall
> right
> > > here in my cubicle so I'm reading right from it.
> >
> > Island Jim
> > Southwest Florida
> > Zone 10
>
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