Jim McKenney
Wed, 13 Jul 2005 12:58:19 PDT
Carol and Marie-Paule,  if your interest in the USDA zoning system is to
find areas in the US with a climate comparable to that in Denmark or
Belgium, you are in for a disappointment. The USDA system is excellent for
the areas for which it was developed, especially the heavily populated parts
of the eastern United States and Canada. The more you move from that area,
the less relevant it becomes. From what I have observed, people on the west
coast of the United States do not use it much - they have better zoning
systems developed in response to their local conditions. For the same
reasons, the European zoning systems are different, too.

The focus of the USDA system is on minimum winter temperature. As every
experienced gardener knows, that is only one of the factors which determine
the success or failure of plants in a given area.

For instance, the dogwood Cornus florida, one of the most beautiful of
eastern North American trees, grows wild as far north as zone 4 southern
Canada (roughly as low as minus 35 C where winters are really winters). Yet
it is difficult to grow well in the much milder English climate (in general,
zone 8 in terms of winter temps) and evidently frequently suffers winter
die-back. Yet dogwood also grows wild and flourishes in zone 8 of the
southeastern United States (and it grows in the highlands of Mexico, too). 

The west coast dogwood, Cornus nuttallii, is generally a failure (actually,
I know of no exceptions) here on the east coast in zone 7. 

USDA Zone 8 London, England, UK and USDA zone 8 Charleston, South Carolina,
USA don't have much in common climatically except the zone 8 assignment. 

The aroid Amorphophallus konjac provides another example. If you had asked
anyone fifty years ago (and some of us are old enough to remember those
days), this plant would have been described as "sub-tropical". Adventurous
gardeners here in zone 7 have been growing and flowering it outside for
decades, and the trials, successful trials, continue to move northward. On
the Alpine-L list, Panayoti Kelaidis today reported the survival of
Amorphophallus konjac in Denver, Colorado, USA, zone 5. 

To paraphrase another contributor to this list, know your local conditions
and don't be satisfied until you have killed a plant yourself several times.

Jim McKenney
Montgomery County, Maryland, USA, USDA zone 7, where three species of palm,
Brugmansia, noisette roses but not Eucomis have grown outside for many

From: []
On Behalf Of Carol Jensen
Sent: Wednesday, July 13, 2005 3:03 PM
To: Pacific Bulb Society; pbs
Subject: Re: [pbs] Usda

At 09:10 13-07-2005, Marie-Paule wrote:
>No, the temperature not always drop to minus 17dgr.C.The temperature is
mostly between -6 and -13.but it not always freezes.
>Thank You for the information,

It looks as though Marie-Paule and I are in the same zone (7). I would put
us both in zone 8, since also in Denmark near the coast where I live, the
winter temperatures are about 10C, enough to freeze the soil January and
February and no more.

Inland in Denmark is colder of course.


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