(WKYT) – Meteorological fall has arrived, but with temperatures in the 90s this week, summertime sizzle is still in full swing. An old piece of weather folklore might indicate when we will see the first frost, but is it accurate?
Be-Leaf-Able Theory
“Goldenrod blooms, frost follows in six weeks” stems from the Farmer’s Almanac, but the theory does have some truth to it.
Michael Wall is the director of the Arboretum, State Botanical Garden of Kentucky. He says goldenrod is a decent predictor of the first frost.
“Goldenrod is what they call photoperiodic, which means that it responds to light in the length of the day in terms of when it flowers,” said Wall. “And so, as the days get shorter, it eventually meets a threshold at which it will start to flower.”
The Kentucky State Flower can also indicate the timing of the first frost in other states.
“You can move north to south, and because of the tilt of the Earth and then the changing of the seasons and all that sort of stuff, it remains accurate kind of throughout its range because the days are longer the further south you are,” said Wall.
Which Species is the Most Accurate?
There are over 100 species of goldenrod in North America and 33 in Kentucky. Each species has different photoperiods and starts flowering at a different time.
“The main goldenrod, your field goldenrod- that’s generally what everybody identifies as being goldenrod- it is roughly six to eight-ish weeks away from when we know, on average, the first frost is,” said Wall.
This species is expected to start blooming in the next week or two in central Kentucky.
“The fancy name for it is Solidago altissima, which is like the field goldenrod. It’s your traditional goldenrod that you’re going to see in any field that’s been abandoned for a while, and it tends to be the one that’s just starting to flower right now, versus other Woodland Goldenrods and species that have started flowering, some of them in late spring,” said Wall.
More Accurate than the Groundhog
Although goldenrod is a decent way of knowing when the first frost will be in many states, not every piece of weather folklore is true. Despite having an entire holiday around whether a groundhog sees its shadow, that theory is not very accurate.
According to data from NOAA’s National Centers for Environmental Information, Punxsutawney Phil has had an accuracy of 35% over the past 20 years. This is determined by using the February and March temperature averages for the U.S. each year.
NOAA tracks 19 groundhogs that have been prognosticating for at least 20 years and are still active prognosticators, comparing their accuracy each year. The most accurate, as of February 2, 2026, is Staten Island Chuck. With an accuracy of 85%, Staten Island Chuck represents New York.
Debunking Allergy Blame
Goldenrod is often blamed for hay fever and fall allergies, but Wall says that the true culprit is ragweed. Both are photoperiodic and flower at the same time.
“Goldenrod has these beautiful yellow flowers. They’re insect-pollinated. All their pollen sticks in the flowers because they’re waiting for insects to come and grab that pollen and take it to another flower,” explained Wall. “Whereas ragweed, when you look at the flowers of ragweed, you question like, is that really flowering? Cause it just looks like this little green thing, and it’s wind-pollinated. It’s blowing off into the breeze, and so that’s what’s getting in your nose and in your eyes and causing all those allergic reactions and allergies.”
First Fall Frost in Lexington
The National Weather Service tracks when different locations have the first and last fall frost each year, using 36 degrees as the temperature cut-off.
In Lexington, the earliest fall frost on record was on September 23, 1896. This record was tied in 1974 and in 2012. The latest first fall frost was on November 9, 1922.
Going by the 1991-2020 climatological normals, the average date for the first 36-degree temperature in Lexington is October 19. There is a 10% chance of the temperature falling to 36 degrees or less before October 6th and a 90% chance of that happening before October 30th.
The first fall freeze tends to be in late October to early November. More frost and freeze data can be found at this link.