Lauw wrote from the south of France, > ...the leaves of Crocus sativus are very > frost resistant: no problems with -10 C > ...during the 20 years I grow them here > I never experienced any frost damage of > the leaves and the corms. Europe is very far north compared to the United States: Madrid is at approximately the same latitude as New York City. Yet much of western Europe is warmer in winter than much of the United States. There are several reasons for this. The Gulf Stream current brings warmer water from the Caribbean to northwestern Europe. Western Europe is closer to the sea than most of the US. And winters in Europe are very cloudy compared to much of the US; clouds prevent heat from escaping, while on cloudless winter nights all the earth's heat can be radiated away. -10C is about 14 F. This corresponds roughly to US Dept of Agriculture zone 8: http://planthardiness.ars.usda.gov/PHZMWeb/ Most gardeners in the US live in areas that are a lot colder than zone 8. There are large parts of the north-central US with winters like those in Russia. Here in Phoenix, elevation about 1,100 feet / 335m in the lower Sonoran Desert, -8C / 18 F occurs at my house. It was very much colder in December 1990, though I didn't have a thermometer then. Our official weather station is at the airport, which is one of the warmest spots in the valley; my low temperatures are routinely 8 F / 4.5C lower than at the airport. Crocus sativus does fine here except for ground squirrels. Beside the temperature problem, much of the US where Crocus sativus might grow gets a large amount of summer rain. I don't know how much a problem this is because I haven't tried growing it with lots of summer rain. Leo Martin Phoenix Arizona USA