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Re: Winter Dormancy

  • Subject: Re: Winter Dormancy
  • From: "W. George Schmid" hostahill@Bellsouth.net
  • Date: Sat, 8 Jan 2005 10:09:46 -0500

Climate of Japan - Hosta dormancy

The ocean climate of Japan is wet and humid and has four distinct seasons.
Hokkaido and other parts of northern Japan have long, harsh winters and
relatively short cool summers. Average temperatures in the northern city of
Sapporo dip to -50C/23F in January but reach only 200C/68F in July. Central
Japan has cold but short winters and hot, humid summers. In Tokyo,
temperatures average 30C/39F in January and 250C/77F in July. Kyushu is
subtropical, with short, mild winters and hot, humid summers. Average
temperatures in the southern city of Kagoshima are 70C/45F in January and
260C/79F) in July. Hosta grow there too! Farther south, the Ryukyu Islands
are warmer still, with frost-free winters - no hostas there!
There are  many other factors: elevation (the above temps are at seacoast
towns), total precipitation, timing of precipitation, soil temperatures,
soil freezing depth, night temperatures, duration of snow cover, and shade.
Spring shade delays soil warming - spring sun advances it. I would say soil
temps are the most important. To say 700 hours below 40 is not science. They
grow hostas in subtropical Italy, but they put them in pots to be exposed to
the much colder night air temps. Another factor is genetic and how the
species have adapted to warmer climates. The central and southern Japanese
hostas do fine in the South given enough summer moisture. Did the cultivar
come from southern species or from northern ones? Or did a particular clone
of H. montana come from the North or South in Japan. They grow all over.
Hostas have a high degree of adaptability. One key seems to be dormancy.
Delayed dormancy might affect growth rates. If the temps are low enough to
trigger normal autumn dormancy, the hostas will probably grow there. If they
get abundant rain in August/September as they do in Japan (not here in the
USA), they can stand higher summer and night temps. No rain and above
350C/over 90F)during late summer/early fall can make them go heat dormant
and they will lose a seasons root growth, hence they will decline (as here
in the South). But given plenty of moisture in late summer in southern
regions seems to make up for the shorter winter cooling periods and earlier
soil warm-up. Up north they may have enough "chilling" but if they dry out
during the critical root growth period they suffer too. It is a combination
of factors!
There are no fast and hard numbers because no one has scientifically
determined what they might be. This would be quite a task, because so many
factors impact the growth rates and survival rates. If anyone out there has
real numbers, determined scientifically, I would like to know about them.
George

W. George Schmid
Hosta Hill - Tucker Georgia USA
Zone 7a - 1188 feet AMSL
84-12'-30" West_33-51' North
Outgoing e-mail virus checked by NAV

----- Original Message -----
From: "Chick" <chick@bridgewoodgardens.com>
To: <hosta-open@hort.net>
Sent: Friday, January 07, 2005 11:17 PM
Subject: Winter Dormancy

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