How hardy do your plants need to be?

Alaska Hardiness The USDA has been publishing Plant Hardiness Zone maps for a while now and the one on the left is for Alaska (click to enlarge). Typing in the zip code for our campus garden (99775) the plant hardiness zone is determined to be 2a : -50 to -45 (F). So that numbers gives us the coldest temperatures for the region which is useful for perennials but not necessarily for annuals. Most seed packets have the information printed on the back and also tell one when to plant the seeds based on the zone. Problem is that starting your seeds following those recommendations does not take the last spring frost in the area into consideration (article here). So here we are getting some help from NOAA who compiles data to determine the average last spring frost with accompanying probabilities. And for Fairbanks (at the College Observatory on campus), the date at which the probability is 10 or less that the temperature drops below 32F is June 7. (The date at the airport in Fairbanks is March 23, quite a bit earlier.) Unfortunately, that information is a bit old as the averages are calculated from data between 1981 and 2005. And since the climate has been changing, this date should be taken with a grain of salt but gives a ballpark to go by.

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