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Iowa · county maple atlas

Maple sugaring in Winneshiek County, Iowa

Winneshiek County had 6 maple operations and 2,314 taps in the 2022 Census, number 2 in Iowa. Around Decorah, sap usually runs from March 4 to April 3. Here's the long-run pattern, 36 seasons of sap weather, and the outlook this week.
Too early to tapAbout 149 days until the usual start.
Sap starts
Mar 4
weather estimate
Season ends
Apr 3
about 4 weeks
Sap days / season
34.4
1991–2026 average
Taps, 2022
2,314
#2 of 32 in IA

Sap-flow outlook at Decorah right now

Full Iowa forecast →

Forecast for Decorah, IA

Updated Oct 6, 9:06 AM EDT

Off-season for now. Sap needs freezing nights, and none are in sight. Winneshiek County's season usually opens around March 4, which is 149 days away.

No freeze-thaw days in the forecast

freeze thaw 32°F

  1. WedOct 7
    53° / 73°

    0h below · 24h above

    No refreeze forecast
  2. ThuOct 8
    48° / 68°

    0h below · 24h above

    No refreeze forecast
  3. FriOct 9
    46° / 69°

    0h below · 24h above

    No refreeze forecast
  4. SatOct 10
    55° / 76°

    0h below · 24h above

    No refreeze forecast
  5. SunOct 11
    61° / 76°

    0h below · 24h above

    No refreeze forecast
  6. MonOct 12
    57° / 66°
    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 Decorah

Freeze-thaw weather at Decorah peaks in the weeks of Mar 2 to Mar 30, which hold about 40% of a season's sap days. March is the busiest month. Note: USDA publishes no season dates for Iowa, so the typical dates here are the raw weather signal. In neighboring states with USDA records, producers reported their seasons running one to three weeks later than this rule.
Typical season: Mar 4 – Apr 30246Week of Dec 1: 1.6 sap days on averageWeek of Dec 8: 1.6 sap days on averageWeek of Dec 15: 1.3 sap days on averageWeek of Dec 22: 1.2 sap days on averageWeek of Dec 29: 0.7 sap days on averageWeek of Jan 5: 1.2 sap days on averageWeek of Jan 12: 0.8 sap days on averageWeek of Jan 19: 0.6 sap days on averageWeek of Jan 26: 0.9 sap days on averageWeek of Feb 2: 1.3 sap days on averageWeek of Feb 9: 1.4 sap days on averageWeek of Feb 16: 1.8 sap days on averageWeek of Feb 23: 1.9 sap days on averageWeek of Mar 2: 2.3 sap days on averageWeek of Mar 9: 2.5 sap days on averageWeek of Mar 16: 3.2 sap days on averageWeek of Mar 23: 3.3 sap days on averageWeek of Mar 30: 2.6 sap days on averageWeek of Apr 6: 1.8 sap days on averageWeek of Apr 13: 1.2 sap days on averageWeek of Apr 20: 0.7 sap days on averageWeek of Apr 27: 0.3 sap days on averageWeek of May 4: 0.1 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 ~Mar 4
Average number of freeze-thaw sap days in each week of the season at Decorah, 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 Mar 4; the middle half of seasons fell between Feb 26 and Mar 10. Earliest Feb 6 (2024), latest Mar 23 (2013).
Closing signal
Median Apr 3; middle half between Mar 27 and Apr 8. Earliest Mar 11 (2012), latest Apr 25 (2013).
Sap days by month
Dec18%Jan11%Feb18%Mar36%Apr16%May1%

36 seasons of sap weather

Winneshiek County seasons, 1991–2026

The best sap year at Decorah was 2002 with 55 freeze-thaw days; the leanest was 2010 with 12. 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 19, 34 sap days3420252025: Feb 19 – Mar 25, 41 sap days4120242024: Feb 6 – Mar 12, 51 sap days5120232023: Mar 7 – Apr 8, 46 sap days4620222022: Mar 13 – Apr 17, 43 sap days4320212021: Feb 26 – Apr 2, 39 sap days3920202020: Mar 4 – Apr 7, 48 sap days4820192019: Mar 5 – Apr 4, 32 sap days3220182018: Mar 22 – Apr 21, 52 sap days5220172017: Feb 22 – Mar 23, 25 sap days2520162016: Feb 20 – Mar 27, 37 sap days3720152015: Feb 27 – Mar 29, 18 sap days1820142014: Mar 17 – Apr 19, 35 sap days3520132013: Mar 23 – Apr 25, 34 sap days3420122012: Feb 11 – Mar 11, 41 sap days4120112011: Mar 6 – Apr 5, 23 sap days2320102010: Mar 3 – Mar 30, 12 sap days1220092009: Mar 4 – Apr 8, 28 sap days2820082008: Mar 16 – Apr 15, 19 sap days1920072007: Feb 21 – Mar 21, 31 sap days3120062006: Mar 3 – Mar 27, 36 sap days3620052005: Feb 28 – Mar 27, 30 sap days3020042004: Feb 27 – Apr 3, 42 sap days4220032003: Feb 26 – Mar 31, 27 sap days2720022002: Mar 4 – Apr 7, 55 sap days5520012001: Mar 14 – Apr 4, 22 sap days2220002000: Feb 9 – Mar 15, 39 sap days3919991999: Feb 25 – Mar 27, 38 sap days3819981998: Mar 20 – Mar 25, 21 sap days2119971997: Mar 9 – Apr 13, 33 sap days3319961996: Mar 12 – Apr 11, 38 sap days3819951995: Feb 26 – Apr 2, 31 sap days3119941994: Mar 9 – Apr 8, 37 sap days3719931993: Mar 19 – Apr 21, 29 sap days2919921992: Mar 6 – Apr 5, 38 sap days3819911991: Mar 1 – Apr 1, 34 sap days34
Each bar runs from the season's opening signal to its closing signal, estimated from daily temperatures at Decorah. Dashed lines mark the typical dates. The right column counts freeze-thaw sap days from December through May.

Maple production

Winneshiek County in the Census of Agriculture

USDA counts maple operations every five years. In Winneshiek County the 2022 Census found 6 farms making syrup (+100% since 2017). That works out to about 0.38 gallons of syrup per tap in 2022. Among the 385 counties in this atlas, Winneshiek County ranks 245 by taps.

Winneshiek County maple production, 2017 and 2022 (USDA Census of Agriculture)
Census yearFarmsTapsGallons of syrupGal / tap
202262,3148880.38
20173withheldwithheld—

“Withheld” means USDA suppressed the figure to avoid disclosing data for individual operations; the farm count is still published.

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 Decorah (974ft), 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. 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 — Iowa, 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

Winneshiek County sugaring questions

When should I tap maple trees in Winneshiek County, Iowa?
In a typical year the sap starts running around March 4 near Decorah and the season winds down around April 3. 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 6 and as late as Mar 23.
How much maple syrup does Winneshiek County produce?
The 2022 Census of Agriculture counted 6 maple operations in Winneshiek County with 2,314 taps producing 888 gallons of syrup, ranking 2 of 32 Iowa's counties with published tap counts.
How many sap days does Winneshiek County get in a season?
On average 34.4 freeze-thaw sap days from December through May at Decorah, of which about 12.4 are textbook days with a night in the 20s and a day in the 40s. The best season since 1991 was 2002 (55 sap days); the leanest was 2010 (12).
Where do these dates come from?
From 36 seasons of daily high and low temperatures at Decorah (PRISM 4-km grid), scored with the same freeze-thaw rule as our live forecast, then calibrated against USDA's reported season dates for Iowa. 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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