Illinois
Planting zones in Stephenson County, Illinois
This county spans USDA zones 5a to 5b, so there is no single zone for Stephenson County and anyone who gives you one is rounding. 86% of its ZIP codes are zone 5a; the rest are not.
Your ZIP code
Get the exact answer for your address
Everything above describes Stephenson County, Illinois as a whole. Hardiness zones and freeze dates are published per ZIP code, so yours is exact — enter it and this page will tell you your zone, which NOAA station it comes from and how far away that station is.
The growing season in Stephenson County is closing
Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives October 9 – October 14 across the 4 NOAA stations serving this county .
Your next season already has a date
The first job of it is 🧅 Green Onions, start indoors, around March 1 – March 4 — counted back from a last spring freeze of April 26 – April 29 here.
These are ranges across the whole county. The ZIP lookup above gives the dates from your own nearest station instead.
All 4 stations agreeAt least one station
Every one of the 4 NOAA stations serving this county counts April 29 – October 9 as growing season (163 days). Widening to any single station gives April 26 – October 14 (171 days).
Which zone you are in depends where you are
Stephenson County covers 2 hardiness zones. A guide that gives the county one zone has picked whichever is largest and rounded everyone else into it — fine for the 86% in zone 5a and wrong for the other 14%. Here is the actual split.
| Zone | ZIP codes | Share | |
|---|---|---|---|
| 5a | 12 | 86% | |
| 5b | 2 | 14% |
Zones are published per ZIP code, so yours is exact even though the county's is not. The hardiness tool will tell you which one you are in.
Your freeze dates
Across the 4 NOAA stations serving this county. These are medians — half of years freeze later than the date shown — so treat the later end of each range as the cautious one.
The growing season runs 165–170 days depending which station you are nearest, as published by NOAA rather than computed from the dates above. Summer highs average 80.4–81.4 °F in June–August. Summer rain over the same months runs 13.7–14.8" across those 4 stations, against the rough inch a week — about 13 inches over the same 92 days — that a vegetable garden is usually reckoned to want. At the middle station that is covered, so watering in Stephenson County is for the gaps between storms rather than the whole season. The inches are NOAA's published normals; the inch a week is a rule of thumb, and it takes no account of a 81 °F summer afternoon drying the soil faster than a cool one.
Every ZIP code in Stephenson County
Zones are published per ZIP code, not per county, so this is the exact answer rather than the county's average. The station column is the nearest one to that ZIP code's centroid and how far away it is — the same figure the tools use, shown here so you can see which ZIP codes are well covered and which are reaching.
| ZIP code | USDA zone | Nearest NOAA station | Distance |
|---|---|---|---|
| 61013 | 5a | Freeport Waste Wtp, IL | 9.1 km |
| 61018 | 5a | Freeport Waste Wtp, IL | 13.8 km |
| 61019 | 5a | Brodhead WWTP, WI | 20.0 km |
| 61027 | 5a | Freeport Waste Wtp, IL | 13.1 km |
| 61032 | 5a | Freeport Waste Wtp, IL | 3.6 km |
| 61039 | 5b | Freeport Waste Wtp, IL | 14.9 km |
| 61044 | 5a | Stockton 3 Nne, IL | 10.8 km |
| 61048 | 5a | Stockton 3 Nne, IL | 12.4 km |
| 61050 | 5a | Monroe WWTP, WI | 18.6 km |
| 61060 | 5a | Monroe WWTP, WI | 14.0 km |
| 61062 | 5a | Freeport Waste Wtp, IL | 19.8 km |
| 61067 | 5b | Freeport Waste Wtp, IL | 10.9 km |
| 61070 | 5a | Freeport Waste Wtp, IL | 17.1 km |
| 61089 | 5a | Stockton 3 Nne, IL | 16.0 km |
ZIP-code positions are area centroids, so a large rural ZIP code's listed distance is measured from the middle of its area rather than from any particular address in it.
When to start seeds in Stephenson County
Every date below is anchored on the last spring freeze at each station and reported as a range across all 4 of them, because no one station speaks for the county.
| Crop | Job | When | Offset |
|---|---|---|---|
| 🧅 Green Onions | Start indoors | March 1 – March 4 | 8 wk before |
| 🌶️ Peppers | Start indoors | March 1 – March 4 | 8 wk before |
| 🥦 Broccoli | Start indoors | March 15 – March 18 | 6 wk before |
| 🥬 Cabbage | Start indoors | March 15 – March 18 | 6 wk before |
| 🥬 Collards | Start indoors | March 15 – March 18 | 6 wk before |
| 🥬 Kale | Start indoors | March 15 – March 18 | 6 wk before |
| 🥬 Leaf Lettuce | Start indoors | March 15 – March 18 | 6 wk before |
| 🫛 Peas | Direct sow | March 15 – March 18 | 6 wk before |
| 🥬 Spinach | Direct sow | March 15 – March 18 | 6 wk before |
| 🍠 Sweet Potato | Start indoors | March 15 – March 18 | 6 wk before |
| 🍅 Tomatoes | Start indoors | March 15 – March 18 | 6 wk before |
| 🥬 Bok Choy | Start indoors | March 22 – March 25 | 5 wk before |
| 🥬 Kohlrabi | Start indoors | March 22 – March 25 | 5 wk before |
| 🥬 Swiss Chard | Start indoors | March 22 – March 25 | 5 wk before |
| 🥬 Arugula | Direct sow | March 29 – April 1 | 4 wk before |
| 🥬 Baby Salad Greens | Direct sow | March 29 – April 1 | 4 wk before |
| 🥕 Beets | Direct sow | March 29 – April 1 | 4 wk before |
| 🧅 Green Onions | Direct sow | March 29 – April 1 | 4 wk before |
| 🥬 Mustard Greens | Direct sow | March 29 – April 1 | 4 wk before |
| 🌶️ Okra | Start indoors | March 29 – April 1 | 4 wk before |
| 🌱 Radishes | Direct sow | March 29 – April 1 | 4 wk before |
| 🥔 Turnips | Direct sow | March 29 – April 1 | 4 wk before |
| 🥬 Cabbage | Set out | April 5 – April 8 | 3 wk before |
| 🥕 Carrots | Direct sow | April 5 – April 8 | 3 wk before |
| 🥬 Collards | Direct sow | April 5 – April 8 | 3 wk before |
| 🥬 Collards | Set out | April 5 – April 8 | 3 wk before |
| 🥒 Cucumbers | Start indoors | April 5 – April 8 | 3 wk before |
| 🧅 Green Onions | Set out | April 5 – April 8 | 3 wk before |
| 🥬 Kale | Direct sow | April 5 – April 8 | 3 wk before |
| 🥬 Kale | Set out | April 5 – April 8 | 3 wk before |
| 🥬 Kohlrabi | Direct sow | April 5 – April 8 | 3 wk before |
| 🥬 Kohlrabi | Set out | April 5 – April 8 | 3 wk before |
| 🥬 Leaf Lettuce | Direct sow | April 5 – April 8 | 3 wk before |
| 🎃 Pumpkins | Start indoors | April 5 – April 8 | 3 wk before |
| 🎃 Summer Squash | Start indoors | April 5 – April 8 | 3 wk before |
| 🎃 Winter Squash | Start indoors | April 5 – April 8 | 3 wk before |
| 🥒 Zucchini | Start indoors | April 5 – April 8 | 3 wk before |
| 🥬 Bok Choy | Direct sow | April 12 – April 15 | 2 wk before |
| 🥬 Bok Choy | Set out | April 12 – April 15 | 2 wk before |
| 🥦 Broccoli | Set out | April 12 – April 15 | 2 wk before |
| 🌿 Cilantro | Direct sow | April 12 – April 15 | 2 wk before |
| 🥬 Leaf Lettuce | Set out | April 12 – April 15 | 2 wk before |
| 🥬 Swiss Chard | Direct sow | April 12 – April 15 | 2 wk before |
| 🥬 Swiss Chard | Set out | April 12 – April 15 | 2 wk before |
| 🌿 Dill | Direct sow | April 19 – April 22 | 1 wk before |
| 🫘 Bush Beans | Direct sow | May 3 – May 6 | 1 wk after |
| 🥒 Cucumbers | Set out | May 3 – May 6 | 1 wk after |
| 🎃 Pumpkins | Direct sow | May 3 – May 6 | 1 wk after |
| 🎃 Pumpkins | Set out | May 3 – May 6 | 1 wk after |
| 🎃 Summer Squash | Direct sow | May 3 – May 6 | 1 wk after |
| 🎃 Summer Squash | Set out | May 3 – May 6 | 1 wk after |
| 🌽 Sweet Corn | Direct sow | May 3 – May 6 | 1 wk after |
| 🍅 Tomatoes | Set out | May 3 – May 6 | 1 wk after |
| 🎃 Winter Squash | Direct sow | May 3 – May 6 | 1 wk after |
| 🎃 Winter Squash | Set out | May 3 – May 6 | 1 wk after |
| 🥒 Zucchini | Direct sow | May 3 – May 6 | 1 wk after |
| 🥒 Zucchini | Set out | May 3 – May 6 | 1 wk after |
| 🥒 Cucumbers | Direct sow | May 10 – May 13 | 2 wk after |
| 🌶️ Okra | Direct sow | May 10 – May 13 | 2 wk after |
| 🌶️ Okra | Set out | May 10 – May 13 | 2 wk after |
| 🌶️ Peppers | Set out | May 10 – May 13 | 2 wk after |
| 🫘 Southern Peas | Direct sow | May 10 – May 13 | 2 wk after |
| 🍠 Sweet Potato | Set out | May 10 – May 13 | 2 wk after |
Offsets are published guidance; the dates they land on are computed from measured NOAA normals. The seed-starting tool does this for your own ZIP code and counts the days.
What survives the winter changes across Stephenson County
Zone 5a carries 48 of 74 perennial edibles; zone 5a carries 48.
Hardiness ranges are a judgement, published by growers rather than measured; the zone they are compared against is measured. On a warm-end verdict, check with your local extension service — a coastal zone 8 and an inland zone 8 are not the same summer.
Cautious — shortens the seasonMedian across stationsOptimistic
- Last spring freeze
- Plan to May 14 to be careful. Median April 26 – April 29 across 4 stations; April 11 is the optimistic end.
- First fall freeze
- Plan to September 26 to be careful. Median October 9 – October 14 across 4 stations; October 29 is the optimistic end.
NOAA publishes these as probabilities, not averages — the middle figure is a median, so half of years fall either side of it. The cautious end is the 10% tail: in roughly nine years in ten the freeze falls on the safe side of it.
The 4 stations behind these numbers
All 4 NOAA stations whose normals this page quotes, spanning about 36 km north to south. Every one is named with its identifier in the station list below — this page does not single one out, because no one station speaks for a whole county.
A relative sketch, not a map with a projection: longitude is adjusted for latitude so the shape is not stretched, and there is no basemap. For the one station nearest a specific address, with its real distance, use the ZIP lookup above.
These are the stations this county's ZIP codes actually cite as nearest — not a claim that each one sits inside its boundary, since a rural ZIP legitimately reaches over it. Every figure above comes from them, and each is named so you can check it.
| Station | NOAA ID | Last spring freeze | First fall freeze | Season |
|---|---|---|---|---|
| Brodhead WWTP, WI | USC00471078 | April 29 | October 12 | 165 days |
| Freeport Waste Wtp, IL | USC00113262 | April 26 | October 13 | 169 days |
| Monroe WWTP, WI | USC00475573 | April 27 | October 14 | 170 days |
| Stockton 3 Nne, IL | USC00118293 | April 27 | October 9 | 165 days |
These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.
Your own ZIP
Work out your own dates
This page describes a whole county. Every tool below answers for one ZIP code, which is the grain the underlying data is published at.
Other places to compare
Stephenson County sits in Illinois. That page carries the whole state's zone spread, its metro areas, and every other county in it with a page here.
More of Illinois
- Lee County, IL 5b
- Shelby County, IL 6a–6b
- Jefferson County, IL 6b
- Wayne County, IL 6b
- Whiteside County, IL 5b
- Williamson County, IL 7a
- White County, IL 6b–7a
- Fayette County, IL 6b
- Jo Daviess County, IL 5a
- Morgan County, IL 6a
- Warren County, IL 5b
- Carroll County, IL 5a–5b
Counties with the same zones — 5a–5b
Matched on the exact zone set, not a dominant zone, so the winter answer on these pages really is the same one as here.
Gear
If you want to act on this
Each link opens an Amazon search rather than a product we picked. We have not tested these and do not rank them — the search is the honest version, and you choose.
- Trunk wrapZone 5a is cold enough that winter sun on a young trunk does more damage than the cold does.
- Row cover and frost clothThe season here closes at the first fall freeze dated above — a cover buys back some of those days at the end.
- MulchFor the perennials nearest their cold limit in zone 5a, where an insulated crown is what decides whether they come back.
As an Amazon Associate we earn from qualifying purchases. That costs you nothing extra, and it buys no influence over anything on this site: the dates come from NOAA normals and the zones from the USDA, and no product affects either.
Sources
Where these numbers come from
Hardiness zones are the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. Freeze dates and growing-season lengths are NOAA 1991–2020 Climate Normals, taken per station and cited above by name and NOAA ID.
County boundaries come from the Census ZCTA-to-county relation, which is what places each ZIP code — and which treats parishes, boroughs and census areas as county equivalents. No station is chosen to represent this county: every range above is taken across all of them and the count is stated, because picking one would be a judgement dressed as a measurement.