Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 61077 — Seward, IL

ZIP code 61077 (Seward, Winnebago County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 24 and the first fall frost October 17.

Where ZIP 61077 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone5b−15 to −10 °F
Coldest night−26.1 to −23.3 °C
Last frostApr 24
First frostOct 17
2012 zone5a

Was 5a on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Seward, IL…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Seward, IL

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 24median — 50% chance of a later frost
Safe for tender plantsMay 8only 10% chance of frost after
First fall frostOctober 17median — 10% chance by Oct 2
Growing season174 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 13 and returns around October 28.

From the NOAA station Rockford Gtr Rockford Airport, IL — 14 miles away, elevation 732 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 61077

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 13 – Mar 27
SpinachSow outdoors · Mar 13 – Apr 3
Broccoli, cabbageStart indoors · Feb 13 – Feb 27
Broccoli, cabbageTransplant · Apr 3 – Apr 17
Onion setsPlant outdoors · Mar 27 – Apr 10
PotatoesPlant outdoors · Apr 3 – Apr 17
LettuceSow outdoors · Mar 27 – Apr 10
Carrots, beetsSow outdoors · Apr 3 – Apr 17
TomatoesStart indoors · Feb 27 – Mar 13
TomatoesTransplant · May 1 – May 15
Peppers, eggplantStart indoors · Feb 13 – Feb 27
Peppers, eggplantTransplant · May 8 – May 22
BeansSow outdoors · May 1 – May 15
Sweet cornSow outdoors · May 1 – May 15
Cucumbers, squashSow outdoors · May 1 – May 15
Fall lettuce, spinachSow outdoors · Aug 22 – Sep 5
GarlicPlant cloves · Oct 3 – Nov 7
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 24) and first fall frost (Oct 17) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 61077 came on Mar 28 — 13 days earlier than the 1991–2020 average (Apr 10).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 5b in Illinois

584 plants native to the lower 48 states, recorded in Illinois, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. Each links to its USDA PLANTS profile.

Trees 77

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican beech80 ft · blooms mid spring · low shade tolerance · to −44 °FAmerican chestnut115 ft · blooms early summer · high shade tolerance · to −33 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °Farborvitae50 ft · blooms mid spring · medium shade tolerance · to −33 °F

Shrubs 102

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAllegheny serviceberry35 ft · blooms early spring · low shade tolerance · to −38 °Falternateleaf dogwood25 ft · blooms mid spring · low shade tolerance · to −47 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican hazelnut10 ft · blooms spring · medium shade tolerance · to −33 °FAmerican holly40 ft · blooms mid spring · low shade tolerance · to −20 °F

Wildflowers & perennials 210

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican licorice4 ft · blooms late spring · medium shade tolerance · to −38 °FAmerican lotus3 ft · blooms mid summer · high shade tolerance · to −36 °FAmerican pokeweed7 ft · blooms mid summer · low shade tolerance · to −33 °F

Grasses 173

American beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °FBailey's sedge2.1 ft · blooms late spring · low shade tolerance · to −33 °Fbeaked sedge4 ft · blooms late spring · low shade tolerance · to −38 °Fbeaked spikerush3 ft · blooms late spring · high shade tolerance · to −28 °F

Vines 7

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Ffrost grape83 ft · blooms late spring · medium shade tolerance · to −23 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fsummer grape30 ft · blooms late spring · low shade tolerance · to −23 °Ftrumpet honeysuckle16 ft · blooms late summer · low shade tolerance · to −33 °F

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Seward, IL.

Soil in Seward, IL

The soil mapped at the center of ZIP 61077 is Osco — silt loam, well drained.

TextureSilt loama good balance for most vegetables
pH6.0slightly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3.5%moderate
Hydrologic groupBwater soaks in moderately
Farmland classprime farmlandUSDA classification

Map unit: Osco silt loam, 2 to 5 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 61077; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Seward, IL

Summer high84 °Faverage high, July
Winter low15 °Faverage low, January
Hot days15days a year at 90 °F or more
Freezing nights136nights a year at 32 °F or less
Growing degree days3,083base 50 °F — the season’s usable heat
Longest day15 h 16 mindaylight on June 21
Shortest day9 h 05 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation37.6 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 29 °F, low 15 °F 29°15° JanFebruary: average high 33 °F, low 18 °F 33°18° FebMarch: average high 47 °F, low 28 °F 47°28° MarApril: average high 60 °F, low 39 °F 60°39° AprMay: average high 71 °F, low 50 °F 71°50° MayJune: average high 81 °F, low 60 °F 81°60° JunJuly: average high 84 °F, low 64 °F 84°64° JulAugust: average high 82 °F, low 62 °F 82°62° AugSeptember: average high 75 °F, low 54 °F 75°54° SepOctober: average high 62 °F, low 42 °F 62°42° OctNovember: average high 47 °F, low 31 °F 47°31° NovDecember: average high 34 °F, low 20 °F 34°20° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 1.70 in precipitation 1.7 JanFebruary: 1.65 in precipitation 1.6 FebMarch: 2.27 in precipitation 2.3 MarApril: 3.73 in precipitation 3.7 AprMay: 4.46 in precipitation 4.5 MayJune: 5.16 in precipitation 5.2 JunJuly: 4.02 in precipitation 4.0 JulAugust: 4.22 in precipitation 4.2 AugSeptember: 3.55 in precipitation 3.5 SepOctober: 2.74 in precipitation 2.7 OctNovember: 2.26 in precipitation 2.3 NovDecember: 1.88 in precipitation 1.9 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Rockford Gtr Rockford Airport, IL (14 mi away); precipitation: New Millford 3.3 W, IL (12 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

610885b
Winnebago, IL · 5 mi
610635b
Pecatonica, IL · 5 mi
610475b
Leaf River, IL · 7 mi
610395b
German Valley, IL · 7 mi
610675b
Ridott, IL · 8 mi
610105b
Byron, IL · 8 mi
611025b
Rockford, IL · 10 mi
611065b
Rockford, IL · 11 mi

Illinois planting zones →

Questions about 61077

What planting zone is ZIP code 61077?

ZIP code 61077 (Seward, IL) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Seward, IL?

The median last spring frost (32 °F) near 61077 is April 24; after May 8 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Rockford Gtr Rockford Airport station.

When is the first frost in Seward, IL?

The median first fall frost near 61077 is October 17, giving a median frost-free growing season of 174 days.

When should I plant tomatoes in 61077?

Start tomato seeds indoors around Feb 27 – Mar 13 and set transplants outside around May 1 – May 15, one to three weeks after the median last frost.

How much rain and snow does 61077 get?

About 37.6 inches of precipitation a year (NOAA 1991–2020 normals, New Millford 3.3 W station).

How hot do summers get in Seward, IL?

The average high peaks at 84 °F in July, with about 15 days a year at 90 °F or more.

What kind of soil does 61077 have?

The USDA soil survey maps Osco at the center of ZIP 61077: silt loam, well drained, pH about 6.0 (slightly acidic).

Did spring come early in Seward, IL in 2026?

Spring leaf-out near 61077 came on Mar 28 in 2026, 13 days earlier than the 1991–2020 average (Apr 10), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Seward, IL?

Long-day onions: the longest day near 61077 is 15 h 16 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 61077 change?

Yes. The 2012 USDA map put 61077 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.