1936 usda zones, US

Michael Mace michaelcmace@gmail.com
Wed, 10 May 2017 09:17:21 PDT
Shmuel asked:

 

>>The chart combining cold and wet has

Coldest Winter Month lows average. This is a puzzle to me as to how to use

that info. Is it the average of coldest temp for that month? Isn't the

actual lowest temperature more important? I live in Jerusalem - C3 on the

chart which has lows average of 40-45 F. Yet we have consistently weeks

with nights at freezing, one or two snows a year, sometimes getting a few

inches. 

 

Very good point. The short answer is that the zones show monthly average
lows because that's all the data I could find online. There are some tricks
you can use to make guesses about lowest temperature, which I'll explain
below.

 

The details:

 

To build the summer-dry maps, you need information on temps and rainfall, by
month, for a very large number of places. You map those spots, and then
connect them together into zones through guesswork. The more data points you
can find about different places on the map, the better the maps will be.

 

The only info I could find with enough geographic density to make maps was
weather station info, which usually has monthly high and low temperatures
and rainfall. There wasn't any "lowest temp ever" data for most of the
places.

 

Because of this, one of the flaws of the Mediterranean climate charts is
that they don't show those occasional deep lows. Unfortunately, those vary
by continent. From what I understand, because Australia and South Africa
both have ocean to the south, it's very unusual for them to get occasional
deep freezes - the ocean moderates the really cold weather.

 

On the other hand, western North America and the Mediterranean have a lot of
land to the north, and you can get storms that come down out of the arctic
with very cold air. I suspect the same may happen in Chile with weather
coming up from the south, although I don't have enough info to say for sure.

 

So, how do you deal with this problem if you're growing bulbs?

 

-If you're growing in a greenhouse and have trouble with a particular bulb,
try to mimic the average temperature and rain patterns for that plant's
native zone.

-If you're growing in the ground, protect plants if your winter temps will
go well below the range they are used to.

-If you're in one of those places that gets occasional deep freezes, chances
are you'll need to protect plants from South Africa and Australia if the
freeze is below their average temperature range. But you don't need to worry
as much about North American and Mediterranean climate plants if the low
temps aren't too low or too long-lasting.

-If you can't protect the bulbs against freezing weather, try growing bulbs
that are from a zone that's one or two levels colder than the one you're in.

-Also pay attention to the length of the summer drought. If a bulb is
evolved to get only a three month dry period in summer, six months of
dryness may kill it. And vice-versa.

 

In my opinion, after trying to grow a lot of Mediterranean-climate plants
from all over the world, soil type is at least as important as temperature.
Maybe more so. For example, Bob Nold has learned amazing stuff from
gardening in raised beds near Denver. A lot of it is non-intuitive and very
interesting.

 

In the end, the climate maps are just a guide to give you some ideas, rather
than the final answer on what to do.

 

Hope that helps.

 

Mike

San Jose, CA

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