Climate change has its challenges, but for gardeners in the Cordova area the good news is the growing season is stretching further into the fall, with the typical free season increased by 23 days since 1944, says climate specialist Rick Thoman of the University of Alaska Fairbanks.
That’s up from 99 to 122 days, with most of that increase in the autumn, Thoman said.
In Anchorage the length of the typical freeze free season has increased by 22 days since 1952 — from 129 days to 151 days. This increase is roughly balanced with about equal changes in an earlier last freeze in the spring and a later first freeze in the fall.
Thoman noted that not all areas of the state 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.
“As far as garden crops, it’s important to remember that the freeze-free season length is only one factor,” Thoman said. “Others include the amount of warmth accumulated during the summer, soil temperatures and even the effect of rapidly decreasing solar energy as September progresses. There are a handful of sites that actually show a shortening of the growing season.”
Thoman also noted that there is lessening variability in the length of the growing season.
“Before 1960, there’s lots of variability,” he said. “There’s some really short years. There’s also some really long years, and that variability has really collapsed in the later 20th century.”
For Fairbanks residents, the gardening season is now 32 days longer, from a median of about 90 days to about 120 days. The growing season in Fairbanks measured as the longest consecutive period of time of readings above 32 degrees Fahrenheit at the Fairbanks Experiment Farm at UAF.
Glenna Gannon, an assistant professor of sustainable food systems at UAF, note that the trend toward a longer growing season means it is now possible to grow crops that were once marginal in Interior Alaska. Still the 2023 growing season was a bit shorter than the median in the Fairbanks area, due to a freeze on June 1.
“While 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,” Gannon said.
This farm is an ideal location and growing conditions in the Tanana Valley are highly dependent on microclimates, she said. 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.
The biggest change to what we can grow here is more about being able to select varieties and certain crops with slightly longer days-to-maturity than we have been able to historically, Gannon said.
“For 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.”
