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For skiers, February may be the peak of winter, but maritime gardeners are moving on to spring. In Seattle, we have a wonderfully early last frost date, especially considering how far north we are. Seattle’s actual last frost date depends on the year, of course, but many books and websites publish dates based on averages over a couple of years. At least, that’s how I hope they get to their conclusions- some people may just guess. Last frost date is sometimes reported as the day when there is less than a 10% chance of temperatures below 28 degrees until fall. Or, sometimes it’s below 32 degrees. What day folks come up also depends on which years they’re taking their data from. Usually in science the more data you have the better, but with a changing climate and increasingly good measurement and record keeping methods, going back too far may skew the results. In any case, I like to think of Seattle’s last frost date as April 1st, because it’s a day I can remember, and it lines up pretty well with what the National Climatic Data Center reports, for both the 28 degree and 32 degree measures.