As we're blanketed here in the Northeast by yet another massive snowstorm, many people are just so sure that we're having a winter of historic proportions. It appears, however, that we may have just become weather wimps who can no longer fathom the kind of real cold gardeners of previous eras considered exceptional.
Most contemporary gardeners here in New York City are aware that the USDA has recently raised our Plant Hardiness Zone to 7B — the former cold hardiness of places much further south, like the North Carolina Piedmont. New York City was previously a much colder zone 6B.
I was questioning the wisdom of that change now that we have experienced the 'polar vortex'. How do this year's lows stack up against historic lows? Are we indeed 7B, or was that zone change a bit premature?
Well, the temperature lows (how these things are determined) for zone 6B are in the range of zero to minus-five degrees Fahrenheit. I couldn't recall temps that low this year, so I checked the records. So far, the coldest temperature we have experienced is 4 degrees Fahrenheit in Central Park on the morning of January 7th. We hit 5 degrees once on January 23rd and experienced single digits a total of just seven times this year. We have yet to dip below zero.
The 4 degree mark should technically put us in zone 7A (zero to five degrees Fahrenheit), but since everyone seems to agree that this is an abnormally cold year — one not likely to happen again for decades — it seems highly unlikely that, with global warming, we will ever see that temperature in New York City again. So, yes, we are now Plant Hardiness Zone 7B — a hardiness zone that was formerly reserved for southern states.
Our milder winters are further confirmed by the shorter duration of cold spells. According to an article in the New York Times, the longest span of continuous temperatures below freezing this year is just 6 days, which is "less than half as long as the freezing periods in the 1970s."
Apparently, our cold sensation is somewhat relative — we've become so accustomed to mild winters that we no longer know what truly historic cold feels like. Or have we just been listening to TV meteorologists' exaggerated 'feels like' temps for far too long?