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Michigan · county maple atlas

Maple sugaring in Shiawassee County, Michigan

Shiawassee County had 9 maple operations and 4,240 taps in the 2022 Census. Around Corunna, sap usually runs from February 23 to March 28. Here's the long-run pattern, 36 seasons of sap weather, and the outlook this week.
Too early to tapAbout 140 days until the usual start.
Sap starts
Feb 23
typical year
Season ends
Mar 28
about 5 weeks
Sap days / season
38.8
1991–2026 average
Taps, 2022
4,240
#37 of 66 in MI

Sap-flow outlook at Corunna right now

Full Michigan forecast →

Forecast for Corunna, MI

Updated Oct 6, 9:49 AM EDT

Off-season for now. Sap needs freezing nights, and none are in sight. Shiawassee County's season usually opens around February 23, which is 140 days away.

No freeze-thaw days in the forecast

freeze thaw 32°F

  1. WedOct 7
    54° / 73°

    0h below · 24h above

    No refreeze forecast
  2. ThuOct 8
    47° / 65°

    0h below · 24h above

    No refreeze forecast
  3. FriOct 9
    41° / 67°

    0h below · 24h above

    No refreeze forecast
  4. SatOct 10
    44° / 72°

    0h below · 24h above

    No refreeze forecast
  5. SunOct 11
    53° / 76°

    0h below · 24h above

    No refreeze forecast
  6. MonOct 12
    52° / 72°
    No refreeze forecast

Data: National Weather Service. Verdicts use freeze-thaw thresholds from maple field research; your woods may run a little differently.

When the sap runs

The sugaring calendar at Corunna

Freeze-thaw weather at Corunna peaks in the weeks of Feb 23 to Apr 6, which hold about 50% of a season's sap days. March is the busiest month.
Typical season: Feb 23 – Mar 280246Week of Dec 1: 1.8 sap days on averageWeek of Dec 8: 1.8 sap days on averageWeek of Dec 15: 1.3 sap days on averageWeek of Dec 22: 1.4 sap days on averageWeek of Dec 29: 1.1 sap days on averageWeek of Jan 5: 1.3 sap days on averageWeek of Jan 12: 0.8 sap days on averageWeek of Jan 19: 0.8 sap days on averageWeek of Jan 26: 0.9 sap days on averageWeek of Feb 2: 1.4 sap days on averageWeek of Feb 9: 1.4 sap days on averageWeek of Feb 16: 2.0 sap days on averageWeek of Feb 23: 2.1 sap days on averageWeek of Mar 2: 2.6 sap days on averageWeek of Mar 9: 2.7 sap days on averageWeek of Mar 16: 3.4 sap days on averageWeek of Mar 23: 3.3 sap days on averageWeek of Mar 30: 2.8 sap days on averageWeek of Apr 6: 2.3 sap days on averageWeek of Apr 13: 1.5 sap days on averageWeek of Apr 20: 1.1 sap days on averageWeek of Apr 27: 0.7 sap days on averageWeek of May 4: 0.3 sap days on averageWeek of May 11: 0.1 sap days on averageWeek of May 18: 0.0 sap days on averageWeek of May 25: 0.0 sap days on averageDecJanFebMarAprMaytaps in ~Feb 23
Average number of freeze-thaw sap days in each week of the season at Corunna, 1991–2026. A sap day is an overnight low under 30.2 °F followed by an afternoon high over 37.4 °F. The shaded band is the typical season.

Year-to-year spread

Opening signal
Median Feb 27; the middle half of seasons fell between Feb 21 and Mar 7. Earliest Feb 2 (2017), latest Mar 15 (2018).
Closing signal
Median Mar 31; middle half between Mar 25 and Apr 8. Earliest Mar 3 (2024), latest Apr 18 (1993).
Sap days by month
Dec18%Jan11%Feb18%Mar34%Apr19%May1%

36 seasons of sap weather

Shiawassee County seasons, 1991–2026

The best sap year at Corunna was 2002 with 56 freeze-thaw days; the leanest was 2011 with 25. Seasons that start early tend to end early too: the trees run on the swing between freezing nights and mild days, and heat ends it.
JanFebMarAprMaysap days20262026: Feb 15 – Mar 21, 35 sap days3520252025: Feb 23 – Mar 28, 35 sap days3520242024: Feb 3 – Mar 3, 34 sap days3420232023: Feb 25 – Mar 31, 49 sap days4920222022: Mar 7 – Apr 10, 40 sap days4020212021: Feb 23 – Mar 22, 40 sap days4020202020: Feb 23 – Mar 25, 45 sap days4520192019: Mar 4 – Apr 2, 34 sap days3420182018: Mar 15 – Apr 18, 55 sap days5520172017: Feb 2 – Mar 6, 33 sap days3320162016: Feb 16 – Mar 23, 48 sap days4820152015: Mar 8 – Apr 5, 32 sap days3220142014: Mar 13 – Apr 17, 32 sap days3220132013: Mar 12 – Apr 8, 40 sap days4020122012: Feb 10 – Mar 12, 46 sap days4620112011: Mar 7 – Apr 3, 25 sap days2520102010: Feb 28 – Mar 31, 28 sap days2820092009: Feb 26 – Mar 28, 36 sap days3620082008: Mar 12 – Apr 5, 33 sap days3320072007: Feb 20 – Mar 22, 30 sap days3020062006: Feb 25 – Mar 30, 36 sap days3620052005: Mar 2 – Mar 29, 31 sap days3120042004: Feb 25 – Mar 25, 44 sap days4420032003: Mar 8 – Apr 11, 33 sap days3320022002: Mar 6 – Apr 10, 56 sap days5620012001: Mar 7 – Apr 6, 31 sap days3120002000: Feb 3 – Mar 8, 42 sap days4219991999: Feb 26 – Mar 29, 50 sap days5019981998: Feb 21 – Mar 26, 42 sap days4219971997: Mar 1 – Apr 2, 36 sap days3619961996: Mar 12 – Apr 16, 47 sap days4719951995: Feb 21 – Mar 27, 36 sap days3619941994: Mar 7 – Apr 8, 44 sap days4419931993: Mar 14 – Apr 18, 35 sap days3519921992: Mar 9 – Apr 9, 46 sap days4619911991: Feb 20 – Mar 20, 37 sap days37
Each bar runs from the season's opening signal to its closing signal, estimated from daily temperatures at Corunna. Dashed lines mark the typical dates. The right column counts freeze-thaw sap days from December through May.

Maple production

Shiawassee County in the Census of Agriculture

USDA counts maple operations every five years. In Shiawassee County the 2022 Census found 9 farms making syrup (+200% since 2017), with taps +60% and syrup output +128% over the same five years. That works out to about 0.23 gallons of syrup per tap in 2022 (0.16 in 2017). Among the 385 counties in this atlas, Shiawassee County ranks 205 by taps.

Shiawassee County maple production, 2017 and 2022 (USDA Census of Agriculture)
Census yearFarmsTapsGallons of syrupGal / tap
202294,2409670.23
201732,6504240.16

Nearby

Neighboring maple counties

Distances are between reference towns; typical dates are each county's own estimate.

About these numbers

The season dates are estimated from 36 seasons of daily high and low temperatures for the PRISM 4-km grid cell at Corunna (745ft), scored with the same freeze-thaw rule as our live forecast: a sap day is an overnight low under 30.2 °F followed by an afternoon high over 37.4 °F. Each season's closing signal is the last sap day before accumulated warmth reaches a threshold, and the opening signal sits five weeks before that, never earlier than the first real freeze-thaw week. Tested against 117 state-seasons of USDA-reported dates, the rule lands within 5.5 days of the reported close and 6.6 days of the reported opening on average, and the typical dates shown here are scaled to Michigan's USDA record (12 years). Production figures are copied from the Census as published. Full method, calibration tables and the downloadable dataset →

Sources · 6

  1. 1.2022 Census of Agriculture, County Level Data — Michigan, Table 37: Maple Syrup, 2022 and 2017 · USDA National Agricultural Statistics Service
  2. 2.PRISM daily temperature grids (AN81d, 4 km), accessed 2026-10-05 · PRISM Group, Oregon State University, https://prism.oregonstate.edu
  3. 3.Applied Climate Information System (ACIS) web services · NOAA Regional Climate Centers
  4. 4.USDA NASS maple syrup reports — approximate average season opened and closed dates, 2011–2022 · USDA National Agricultural Statistics Service (mirrored by the University of Vermont)
  5. 5.Sap flow in sugar maple: timing and weather drivers (Frontiers in Agronomy, 2025) · de Lima Santos et al.
  6. 6.GeoNames gazetteer (cities500), CC BY 4.0 · GeoNames

FAQ

Shiawassee County sugaring questions

When should I tap maple trees in Shiawassee County, Michigan?
In a typical year the sap starts running around February 23 near Corunna and the season winds down around March 28. Have your taps in a day or two before the first forecast string of freezing nights and 40 °F days. In the past 36 seasons the weather signal came as early as Feb 2 and as late as Mar 15.
How much maple syrup does Shiawassee County produce?
The 2022 Census of Agriculture counted 9 maple operations in Shiawassee County with 4,240 taps producing 967 gallons of syrup, ranking 37 of 66 Michigan's counties with published tap counts.
How many sap days does Shiawassee County get in a season?
On average 38.8 freeze-thaw sap days from December through May at Corunna, of which about 13.5 are textbook days with a night in the 20s and a day in the 40s. The best season since 1991 was 2002 (56 sap days); the leanest was 2011 (25).
Where do these dates come from?
From 36 seasons of daily high and low temperatures at Corunna (PRISM 4-km grid), scored with the same freeze-thaw rule as our live forecast, then calibrated against USDA's reported season dates for Michigan. They describe a typical year at one point in the county; your sugarbush, slope and elevation can shift them by days.

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