" Isn't the actual lowest temperature more important?" For geophytes, I've always thought that minimum soil temps at depth X were more indicative of ultimate cold hardiness. There are maps of US max frost depths easily available but little info on the associated minimum soil temps. Mark Mazer Hertford, NC On Wed, May 10, 2017 at 12:17 PM, Michael Mace <michaelcmace@gmail.com> wrote: > 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 > > _______________________________________________ > pbs mailing list > pbs@mailman1.ibiblio.org > http://pacificbulbsociety.org/list.php > http://pacificbulbsociety.org/pbswiki/ > _______________________________________________ pbs mailing list pbs@mailman1.ibiblio.org http://pacificbulbsociety.org/list.php http://pacificbulbsociety.org/pbswiki/