One problem with the USDA zones, as Bob notes, is that they do not deal well with steep transitions from one elevation to another. As a result, my former property in the foothills of the Cascade Mountains was on a border between Zone 8 and Zone 1. Another reflection of the fact that these zones were drawn up east of the Rocky Mountains, where a lot of the country is relatively flat, and intended originally to help growers of fruit trees. Eventually Sunset Magazine, a California publication, took the matter in hand and made a new, much more complex zone map for the American west. Though now in "Zone 8," I rarely choose plants with that zone rating because I'm pretty sure they will be killed in one winter in four. Moreover, zone ratings based on winter lows are inadequate: summer atmospheric humidity is also an important factor in plant survival because it affects the differential between daytime and night temperatures. Jane McGary Portland, Oregon, USA On 5/7/2017 10:29 AM, penstemon wrote: >> Bob posted a link to a photograph of a USDA climate zone map from 1936. > Were the temperature ranges for each zone the same then as they are now? > It was Rick’s link. It doesn’t seem to matter what the ranges were. > Much of the northeastern US is shown in the same zone as some of the more frigid parts of Colorado. (Extreme northwestern Colorado.) If that were true, then much of New York, northern New Jersey, and western Connecticut would be devoid of much of any vegetation, because of the continual drops in temperature to –50F (-45.5C) and below. > We probably would have read about that at one time or another. > Bob Nold > Denver, Colorado, USA > _______________________________________________ > 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/