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Iowa · county maple atlas

Maple sugaring in Johnson County, Iowa

Johnson County had 9 maple operations and 370 taps in the 2022 Census, number 4 in Iowa. Around Iowa City, sap usually runs from February 20 to March 26. Here's the long-run pattern, 36 seasons of sap weather, and the outlook this week.
Too early to tapAbout 137 days until the usual start.
Sap starts
Feb 20
weather estimate
Season ends
Mar 26
about 5 weeks
Sap days / season
40.1
1991–2026 average
Taps, 2022
370
#4 of 32 in IA

Sap-flow outlook at Iowa City right now

Full Iowa forecast →

Forecast for Iowa City, IA

Updated Oct 6, 7:46 AM EDT

Off-season for now. Sap needs freezing nights, and none are in sight. Johnson County's season usually opens around February 20, which is 137 days away.

No freeze-thaw days in the forecast

freeze thaw 32°F

  1. WedOct 7
    56° / 78°

    0h below · 24h above

    No refreeze forecast
  2. ThuOct 8
    52° / 70°

    0h below · 24h above

    No refreeze forecast
  3. FriOct 9
    50° / 73°

    0h below · 24h above

    No refreeze forecast
  4. SatOct 10
    57° / 78°

    0h below · 24h above

    No refreeze forecast
  5. SunOct 11
    61° / 79°

    0h below · 24h above

    No refreeze forecast
  6. MonOct 12
    60° / 73°
    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 Iowa City

Freeze-thaw weather at Iowa City peaks in the weeks of Feb 9 to Mar 30, which hold about 50% 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: Feb 20 – Mar 260246Week of Dec 1: 2.3 sap days on averageWeek of Dec 8: 2.5 sap days on averageWeek of Dec 15: 2.1 sap days on averageWeek of Dec 22: 1.7 sap days on averageWeek of Dec 29: 1.3 sap days on averageWeek of Jan 5: 1.6 sap days on averageWeek of Jan 12: 1.3 sap days on averageWeek of Jan 19: 1.1 sap days on averageWeek of Jan 26: 1.6 sap days on averageWeek of Feb 2: 1.6 sap days on averageWeek of Feb 9: 2.0 sap days on averageWeek of Feb 16: 2.3 sap days on averageWeek of Feb 23: 2.4 sap days on averageWeek of Mar 2: 2.5 sap days on averageWeek of Mar 9: 2.9 sap days on averageWeek of Mar 16: 3.2 sap days on averageWeek of Mar 23: 2.8 sap days on averageWeek of Mar 30: 2.1 sap days on averageWeek of Apr 6: 1.5 sap days on averageWeek of Apr 13: 1.0 sap days on averageWeek of Apr 20: 0.3 sap days on averageWeek of Apr 27: 0.1 sap days on averageWeek of May 4: 0.1 sap days on averageWeek of May 11: 0.0 sap days on averageWeek of May 18: 0.0 sap days on averageWeek of May 25: 0.0 sap days on averageDecJanFebMarAprMaytaps in ~Feb 20
Average number of freeze-thaw sap days in each week of the season at Iowa City, 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 20; the middle half of seasons fell between Feb 17 and Feb 26. Earliest Jan 30 (2017), latest Mar 8 (2018).
Closing signal
Median Mar 26; middle half between Mar 14 and Mar 31. Earliest Mar 2 (1992), latest Apr 11 (2018).
Sap days by month
Dec23%Jan15%Feb20%Mar31%Apr11%May0%

36 seasons of sap weather

Johnson County seasons, 1991–2026

The best sap year at Iowa City was 2018 with 67 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 1 – Mar 8, 40 sap days4020252025: Feb 7 – Mar 10, 35 sap days3520242024: Feb 5 – Mar 3, 43 sap days4320232023: Feb 21 – Mar 28, 47 sap days4720222022: Feb 17 – Mar 14, 50 sap days5020212021: Feb 17 – Mar 21, 40 sap days4020202020: Feb 19 – Mar 24, 53 sap days5320192019: Mar 1 – Apr 3, 40 sap days4020182018: Mar 8 – Apr 11, 67 sap days6720172017: Jan 30 – Mar 5, 41 sap days4120162016: Feb 8 – Mar 12, 47 sap days4720152015: Feb 25 – Mar 30, 37 sap days3720142014: Mar 7 – Apr 9, 34 sap days3420132013: Mar 7 – Apr 5, 46 sap days4620122012: Feb 9 – Mar 11, 45 sap days4520112011: Feb 26 – Apr 1, 31 sap days3120102010: Mar 1 – Mar 27, 12 sap days1220092009: Feb 16 – Mar 21, 28 sap days2820082008: Mar 5 – Apr 4, 27 sap days2720072007: Feb 18 – Mar 20, 43 sap days4320062006: Feb 19 – Mar 26, 50 sap days5020052005: Feb 24 – Mar 28, 48 sap days4820042004: Feb 20 – Mar 24, 43 sap days4320032003: Feb 20 – Mar 15, 38 sap days3820022002: Feb 20 – Mar 27, 64 sap days6420012001: Mar 5 – Apr 2, 23 sap days2320002000: Feb 8 – Mar 5, 45 sap days4519991999: Feb 23 – Mar 27, 40 sap days4019981998: Feb 19 – Mar 25, 27 sap days2719971997: Feb 20 – Mar 27, 42 sap days4219961996: Feb 26 – Apr 2, 40 sap days4019951995: Feb 17 – Mar 10, 29 sap days2919941994: Feb 23 – Mar 30, 35 sap days3519931993: Mar 7 – Apr 6, 27 sap days2719921992: Jan 31 – Mar 2, 48 sap days4819911991: Feb 18 – Mar 16, 38 sap days38
Each bar runs from the season's opening signal to its closing signal, estimated from daily temperatures at Iowa City. Dashed lines mark the typical dates. The right column counts freeze-thaw sap days from December through May.

Maple production

Johnson County in the Census of Agriculture

USDA counts maple operations every five years. In Johnson County the 2022 Census found 9 farms making syrup (+800% since 2017). That works out to about 0.13 gallons of syrup per tap in 2022. Among the 385 counties in this atlas, Johnson County ranks 325 by taps.

Johnson County maple production, 2017 and 2022 (USDA Census of Agriculture)
Census yearFarmsTapsGallons of syrupGal / tap
20229370470.13
20171withheldwithheld—

“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 Iowa City (686ft), 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

Johnson County sugaring questions

When should I tap maple trees in Johnson County, Iowa?
In a typical year the sap starts running around February 20 near Iowa City and the season winds down around March 26. 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 Jan 30 and as late as Mar 8.
How much maple syrup does Johnson County produce?
The 2022 Census of Agriculture counted 9 maple operations in Johnson County with 370 taps producing 47 gallons of syrup, ranking 4 of 32 Iowa's counties with published tap counts.
How many sap days does Johnson County get in a season?
On average 40.1 freeze-thaw sap days from December through May at Iowa City, of which about 12.6 are textbook days with a night in the 20s and a day in the 40s. The best season since 1991 was 2018 (67 sap days); the leanest was 2010 (12).
Where do these dates come from?
From 36 seasons of daily high and low temperatures at Iowa City (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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