- frost-free season [period]; frostless season
There are about 150 frost-free days in Changchun every year.
The frost-free period lengthened, and the frost period shortened.
The annual precipitation comes to 506.7 Mm and the frost-free period lasts 189 days.
Northern Alberta is mostly covered by boreal forest and has fewer frost-free days than southern Alberta due to its subarctic climate.
The sunshine duration is long, the temperature difference is big, the frost-free period is long, and the annual solar radiation amount is much, which is good for the growth of crops.
A paper published in the Proceedings of the National Academy of Sciences reported that the ragweed pollen season in North America has been getting longer as the number of frost-free days increases.