Planting zone for 68776 — South Sioux City, NE
ZIP code 68776 (South Sioux City, Dakota County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is April 29 and the first fall frost October 7.
Where ZIP 68776 is
Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoomNot 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.
Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5a means →
Frost forecast — next 7 nights
live from the National Weather ServiceLoading the forecast for South Sioux City, NE…
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 South Sioux City, NE
A hard freeze (28 °F) usually ends around April 19 and returns around October 18.
From the NOAA station Sioux City Ang, IA — 6 miles away, elevation 1,099 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 68776
Counted from the median last spring frost (Apr 29) and first fall frost (Oct 7) 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 68776 came on Mar 19 — 18 days earlier than the 1991–2020 average (Apr 6).
Apr 62026
Mar 19
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).
Soil in South Sioux City, NE
The soil mapped at the center of ZIP 68776 is Haynie — silt loam, moderately well drained.
Map unit: Haynie silt loam, 0 to 2 percent slopes, occasionally flooded.
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 68776; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.
Climate in South Sioux City, NE
Average high and low, by month
Precipitation by month inches
NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Sioux City Ang, IA (6 mi away); precipitation: Sioux City Ang, IA (6 mi away). Daylight is calculated from latitude.
Nearby ZIP codes
All 8 nearest ZIP codes share zone 5a.
Questions about 68776
What planting zone is ZIP code 68776?
ZIP code 68776 (South Sioux City, NE) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).
When is the last frost in South Sioux City, NE?
The median last spring frost (32 °F) near 68776 is April 29; after May 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Sioux City Ang station.
When is the first frost in South Sioux City, NE?
The median first fall frost near 68776 is October 7, giving a median frost-free growing season of 161 days.
When should I plant tomatoes in 68776?
Start tomato seeds indoors around Mar 4 – Mar 18 and set transplants outside around May 6 – May 20, one to three weeks after the median last frost.
How much rain and snow does 68776 get?
About 30.3 inches of precipitation a year (NOAA 1991–2020 normals, Sioux City Ang station).
How hot do summers get in South Sioux City, NE?
The average high peaks at 86 °F in July, with about 27 days a year at 90 °F or more.
What kind of soil does 68776 have?
The USDA soil survey maps Haynie at the center of ZIP 68776: silt loam, moderately well drained, pH about 7.3 (neutral).
Did spring come early in South Sioux City, NE in 2026?
Spring leaf-out near 68776 came on Mar 19 in 2026, 18 days earlier than the 1991–2020 average (Apr 6), according to the USA National Phenology Network Spring Index.
What kind of onions grow in South Sioux City, NE?
Long-day onions: the longest day near 68776 is 15 h 18 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).