Getting Ready To Enter The Last Vermont Spring Frost Countdown

Leaves on a white ash tree in Huntington, Vermont were
left wilted and black after a late season freeze on
May 18, 2023.  However, most recent years in
Vermont have featured earlier and earlier
last spring freezes of the season. 

 It's possible -though unlikely - that warmer spots in Vermont like parts of the Champlain Valley, have seen their last spring frost of the season. 

I say unlikely, because the average date of the last spring frost in Burlington is May 6.  We're defining frost here as a temperature of 32 degrees or lower.

You can still get light frosts at temperatures above 32 degrees, but it's easiest to compare and contrast using that 32 degree reading. 

In Burlington, the latest frost on record was an epic one on May 31, 1961 which sent the temperature all the way down to 25 degrees at the airport in South Burlington.

That 1961 brought temperatures into the low and 20s statewide, with a couple upper teens reported causing exceptionally bad crop damage and turning early summer foliage a depressing brown. That historic freeze caused $500,000 in Vermont crop damage, which corrected for inflation would be more than $5.3 million in today's dollars.

 On the other hand, way back in 1898, the last frost in Burlington was on April 7, the earliest final frost of they season on record. 

If Burlington ended up having its last freeze of the season on April 21 this year (a big if), that would be the earliest last freeze since April 17, 2019.   

The last frost of the spring has been trending earlier than the long term average in recent years and decades, thanks at least in part to climate change. In the last two decades, Burlington's final frost of the spring has come later than the May 6  only five times. 

EARLIER SPRING DANGERS

The fact that we are having earlier springs because of that climate change is making what used to be nearly harmless early to mid-May frosts and freezes more dangerous and damaging. That's because the more intense spring warmth of recent years and decades causes plants to sprout much earlier than they used to. 

A harsh May 18, 2023 freeze caused damage similar to that of that end of May freeze back in 1961, In the 2023 freeze, Vermont suffered extensive damage and losses to crops of apples, grapes, strawberries and other produce. Damage in the Green Mountain State was estimated at a whopping $10 million. 

This year, spring plant growth is running on the early side once again, but not as early as it did in 2023 and several other recent years. That could well save us from damaging freezes this year, unless we get an errant harsh freeze, say, after May 10 or 15.  

Which is always possible. Because generally, we've gotten warmer, but extremes have gotten more, well, extreme, so we could be prone to major temperatures gyrations. 

For the record, there are no hard freezes in the forecast at least through the next week and likely beyond. 

ELSEWHERE IN VERMONT

Elsewhere in Vermont, spring freezes of course come later than in the Banana Belt Champlain Valley. 

Up in St. Johnsbury, the average date of the last spring frost is May 20. But it has gotten to 32 degrees there as late as June 20, 1918.

June, 1918 was remarkably cold in Vermont in a remarkably chilly year. It was 35 degrees in Burlington that June 20, and the city endured 11 days in a row between June 13 and 23 in which the low temperature was below 50 degrees. 

Most other areas of Vermont have had June frosts in the past. Even Burlington has come close, with temperatures of 33 degrees in the Junes of 1924 and 1986. 

Montpelier has had a freeze as late as June 6, 1964. 

Other areas of Vermont tend to have much later spring frosts than the Champlain Valley, The coldest hollows of the Northeast Kingdom have had frost every month of the year. 

In the cold valley of Island Pond, deep in the Northeast Kingdom, the latest "spring" frost was on July 2, 1992. Yep, right before the Fourth of July weekend. 

There was a teeny-tiny ice age of sorts going on in 1992. Mount Pinatubo in the Philippines erupted in June, 1991, spewing so much sulfur dioxide into the upper atmosphere that it temporarily interrupted global warming and cooled the Earth by almost a full degree for a little over a year. 

That does't sound like much, but such a drop is impressive.

So unless there's another enormous volcanic eruption somewhere on Earth, the chances of summer or late spring frosts in Vermont are becoming more and more remote. 

Overall, even though the last spring freezes of the season are tending to come later and later, I'd still obey those old rules about planting your gardens outside. I'd still wait until around Memorial Day or so to put the tomato plants outdoors, for instance.