Minnesota Seasons

Prevernal is the transitional ecological season often referred to as “pre-spring.” It marks the period between the permanent snow cover of the Hibernal season and the first floral blooms of Spring. In Minnesota, this window typically opens around March 1 as average daily high temperatures begin to climb above freezing, initiating the spring thaw.

During this season, the landscape transitions from white to brown as the snowpack recedes, exposing “mud season” and dormant vegetation. Key biological markers include the swelling of buds on deciduous trees—particularly Silver Maples and Willows—and the initial flow of sap.

In the animal kingdom, the season is defined by the return of early-season migrants like Red-winged Blackbirds and the emergence of “snow flies” and stoneflies near open water. The Prevernal season concludes around May 1, as the first ephemeral wildflowers emerge and the landscape begins to ‘green up.’

The estival ecological season represents the peak of the growing year, corresponding roughly to the first half of the summer calendar. In Minnesota, this season typically begins around June 15 and extends to about August 15. During this window, the landscape is characterized by a mature, deep-green canopy as trees reach full leaf expansion.

Biologically, the estival period is the busiest time for avian species, as adults shift from establishing territories to the demanding task of hatching and provisioning their offspring. It is also the season of maximum solar energy capture; high temperatures and long daylight hours drive rapid growth in perennial plants and high insect activity. By the end of the estival season in mid-August, many songbirds begin to go quiet as the nesting cycle concludes, and the first hints of the late-summer ‘serotinal’ shift—such as the ripening of berries and the blooming of prairie grasses—begin to appear.

The serotinal season represents the late-summer transition, corresponding roughly to the second half of the calendar summer. In Minnesota, this ecological window typically begins around August 15 and concludes near September 15. It is a season defined by maturity and preparation rather than growth.

During this period, the deep greens of the estival season begin to fade as deciduous leaves lose chlorophyll and initiate their first subtle shifts in color. On the prairies and in the wetlands, late-blooming species like Goldenrods and Asters reach their peak. For avian populations, the serotinal season is a time of gathering; young birds have reached independence and join adults in ‘staging’—forming large flocks in preparation for the upcoming fall migration. The air often takes on a drier quality, and the first significant cool fronts begin to signal the end of the high-summer heat.

The autumnal season, or fall, is the period of transition from the biological activity of summer to the dormancy of winter. It follows the serotinal season as the landscape begins to shut down in response to decreasing daylight and falling temperatures. In Minnesota, the autumnal season typically begins around September 15 and lasts until approximately December 1, though its peak varies by latitude.

This season is visually defined by the senescence of deciduous leaves, as they reach full color before turning brown and falling. Forbs and grasses also enter dormancy, contributing to a significant change in the landscape’s texture and palette. For avian species, this is the primary window for the southward migration back to wintering habitats.

In the Twin Cities metro area, peak color typically arrives between late September and mid-October. The progression of the season can be monitored via the Minnesota DNR's 'Fall Color Finder,' which tracks the northern-to-southern advancement of peak color across the state. In this ecological context, the autumnal season is considered fully arrived in areas where color is at or past its peak.

The hibernal ecological season corresponds to the winter calendar months and represents the period of deepest dormancy in the Minnesota landscape. In our region, this season typically begins around December 1 and lasts until approximately March 1. It is characterized by sustained sub-freezing temperatures, a generally snow-covered landscape, and an absence of migratory bird species.

The onset of the hibernal season is marked by two primary physical thresholds: the arrival of permanent snow cover and the “deep freeze.” In the Twin Cities, the average date for the first one-inch snowfall is November 18, though “permanent” snow cover—defined as at least one centimeter of snow lasting for at least one month—usually establishes by mid-December. This shift is accompanied by a sharp drop in temperature; by December 3, the average daily high in the metro area typically falls below freezing.

During this season, deciduous trees remain bare as fallen leaves decay beneath the snowpack. Resident wildlife survives through specialized adaptations, while migratory birds have fully settled into their winter habitats. The hibernal season remains the dominant state of the landscape until the first thaws of the prevernal transition in early March.