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Re: Re: temperatures and hardiness

Which is why I always try to buy plants from nurseries here in the midwest...although there are times when the only places I can find what I want is ForestFarm or Plant Delights!
On Monday, April 12, 2004, at 06:15 PM, Marge Talt wrote:

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.
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
Editor:  Gardening in Shade

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