ZONE 1. Coldest Winters in the West and Western Prairie States
Growing season: early June through Aug., but with some variation―the longest seasons are usually found near this zone's large bodies of water. Frost can come any night of the year. Winters are snowy and intensely cold, due to latitude, elevation, and/or influence of continental air mass. There's some summer rainfall.
ZONE 43. Upper Mississippi Valley, Upper Michigan, Southern Ontario and Quebec
Growing season: late May to mid-Sept. The climate is humid from spring through early fall; summer rains are usually dependable. Arctic air dominates in winter, with lows typically from -20 degrees to -30 degrees F/-29 degrees to -34 degrees C.
ZONE 45. Northern Parts of Minnesota and Wisconsin, Eastern Manitoba through Interior Quebec
Growing season: mid-June through Aug., with rain throughout; rainfall (and humidity) are least in zone's western part, greatest in eastern reaches. Winters are frigid (-30 degrees to -40 degrees F/-34 degrees to -40 degrees C), with snow cover, deeply frozen soil.