Later fall freezes, earlier thaws increase Interior AV狼论坛 growing season

A woman in a raincoat smiles while harvesting a bounty of peppers.
Courtesy of Glenna Gannon
Glenna Gannon harvests Red Ember peppers as part of the University of AV狼论坛 Fairbanks Variety Trials Program at the Fairbanks Experiment Farm in September 2021. Longer growing seasons enable different varieties of many vegetables to grow in Interior AV狼论坛.

If Interior AV狼论坛ns have noticed that summer seems to linger long enough to ripen their tomatoes and winter arrives more slowly, they鈥檙e not imagining things. 

Nine of the 10 latest 鈥渇irst freezes鈥 have occurred since 2001. The median first freeze date is now two weeks later than it was pre-World War II, University of AV狼论坛 Fairbanks climate specialist Rick Thoman said. This year, the first freeze was recorded on Sept. 19. 

The trend toward a longer growing season means it鈥檚 now possible to grow crops that were once marginal in Interior AV狼论坛, said Glenna Gannon, assistant professor of sustainable food systems at UAF. She heads up the Variety Trials Program at UAF.

Temperatures have been recorded at the Fairbanks Experiment Farm at UAF since summer 1911. Climate charts can be found on the website.

鈥淪ince 2000, there's lots of years now, though not every one, when the first freeze is the 15th of September or later,鈥 Thoman said. 鈥淲hat we can say is prior to 2001, the latest first freeze at the farm was Sept. 17, 1938.鈥

Coupled with later first freezes is a trend toward earlier last freezes in the spring, he said. That translates to a growing season that is about 32 days longer than since record-keeping began, from a median of about 90 days to about 120 days. The growing season is measured as the longest consecutive period of time of readings above 32 degrees Fahrenheit at the farm鈥檚 weather station.

Thoman said not all areas of AV狼论坛 are seeing shorter springs and longer falls. Some areas are seeing the last freeze coming later in the spring, but less change in the fall, and vice versa. 

鈥淭here鈥檚 a handful of sites that actually show a shortening of the growing season,鈥 he said. 

One other change that鈥檚 standing out to Thoman is the lessening variability in the length of the growing season. 

鈥淏efore 1960, there鈥檚 lots of variability,鈥 he said. 鈥淭here鈥檚 some really short years. There鈥檚 also some really long years, and that variability has really collapsed in the later 20th century.鈥

Fairbanks鈥 far-north location still holds many challenges for farmers. 2023鈥檚 growing season was a bit shorter than the median, due to a freeze on June 1. 

鈥淲hile we still have other high-latitude related challenges to growing certain crops (e.g. cold soils, long photoperiods), we have been successfully trialing field-grown corn (22 varieties), artichokes (five varieties), peppers (14 varieties), musk melons (two varieties) and, as of this summer, tomatoes (16 varieties) at the Fairbanks Experiment Farm,鈥 Gannon said. 

She noted that the experiment farm is in an ideal location and that growing conditions in the Tanana Valley are highly dependent on microclimates. Farms at lower elevations or with ice wedges in the fields only a few miles away may not be as successful with long- or warm-season crops.

鈥淚 think the biggest change to what we can grow here is more about being able to select varieties (or cultivars) and certain crops with slightly longer days-to-maturity than we have been able to historically,鈥 Gannon said. 鈥淔or instance, brassicas are extremely hardy, but a crop like Brussels sprouts takes longer to mature. With the longer growing season, more folks are having an easier time getting Brussels sprouts to mature before the snow and frost fully wipe out their gardens.鈥

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