Place guide
Planting zones in Columbus, OH
This metro spans USDA zones 6a to 6b, so there is no single zone for Columbus, OH and anyone who gives you one is rounding. 56% of its ZIP codes are zone 6b; the rest are not.
Your ZIP code
Get the exact answer for your address
Everything above describes Columbus, OH 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 Columbus, OH is closing
Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives October 10 – October 28 across the 21 NOAA stations serving this metro area .
Your next season already has a date
The first job of it is 🧅 Green Onions, start indoors, around February 20 – March 6 — counted back from a last spring freeze of April 17 – May 1 here.
These are ranges across the whole metro area. The ZIP lookup above gives the dates from your own nearest station instead.
All 21 stations agreeAt least one station
Every one of the 21 NOAA stations serving this metro area counts May 1 – October 10 as growing season (162 days). Widening to any single station gives April 17 – October 28 (194 days).
That is a 32-day difference inside one metro area — which is why this page gives ranges rather than a single planting date. The ZIP lookup above resolves it to one station.
Which zone you are in depends where you are
Columbus, OH covers 2 hardiness zones. A guide that gives the metro one zone has picked whichever is largest and rounded everyone else into it — which is fine for the 56% in zone 6b and wrong for the other 44%. Here is the actual split.
| Zone | ZIP codes | Share | |
|---|---|---|---|
| 6b | 75 | 56% | |
| 6a | 58 | 44% |
Zones are published per ZIP code, so yours is exact even though the metro's is not. The hardiness tool will tell you which one you are in.
Your freeze dates
Those are the earliest and latest medians among the 21 stations serving this metro — not an average, and not one station standing in for the rest. Half of years freeze later than a station's own median.
The spread is the point. Even in a metro that is one hardiness zone throughout, its stations disagree about the last spring freeze. Hardiness zone and frost date measure different things — a zone is the average annual coldest night, a freeze date is when the season turns — and a place can be uniform in one and varied in the other. Use the tools below with your own ZIP rather than the ends of this range.
Your growing season
NOAA publishes a growing-season length for each station, and across the 21 stations serving Columbus, OH it runs 161–192 days . That figure is published, not computed from the two freeze dates — subtracting one from the other gives the wrong answer wherever a season crosses New Year. Mean summer high (June–August) runs 80–85 °F , below the 90 °F point where cool-season crops reliably bolt. Summer rain over the same months runs 10.8–13.3" across those 20 stations, against the rough inch a week — about 13 inches over the same 92 days — that a vegetable garden is usually reckoned to want. The middle station covers about 95% of it, so expect to make up the rest. The inches are NOAA's published normals; the inch a week is a rule of thumb, and it takes no account of a 83 °F summer afternoon drying the soil faster than a cool one.
When to start seeds in Columbus, OH
Every spring job for 63 crop dates, counted from this metro's own last spring freeze. Each is a range across all 21 stations — the earliest and latest that job falls anywhere in the metro — because no one station speaks for the whole area.
| Crop | Job | When | Offset |
|---|---|---|---|
| Green Onions | Start indoors | February 20 – March 6 | 8 weeks before |
| Peppers | Start indoors | February 20 – March 6 | 8 weeks before |
| Broccoli | Start indoors | March 6 – March 20 | 6 weeks before |
| Cabbage | Start indoors | March 6 – March 20 | 6 weeks before |
| Collards | Start indoors | March 6 – March 20 | 6 weeks before |
| Kale | Start indoors | March 6 – March 20 | 6 weeks before |
| Leaf Lettuce | Start indoors | March 6 – March 20 | 6 weeks before |
| Peas | Direct sow | March 6 – March 20 | 6 weeks before |
| Spinach | Direct sow | March 6 – March 20 | 6 weeks before |
| Sweet Potato | Start indoors | March 6 – March 20 | 6 weeks before |
| Tomatoes | Start indoors | March 6 – March 20 | 6 weeks before |
| Bok Choy | Start indoors | March 13 – March 27 | 5 weeks before |
| Kohlrabi | Start indoors | March 13 – March 27 | 5 weeks before |
| Swiss Chard | Start indoors | March 13 – March 27 | 5 weeks before |
| Arugula | Direct sow | March 20 – April 3 | 4 weeks before |
| Baby Salad Greens | Direct sow | March 20 – April 3 | 4 weeks before |
| Beets | Direct sow | March 20 – April 3 | 4 weeks before |
| Green Onions | Direct sow | March 20 – April 3 | 4 weeks before |
| Mustard Greens | Direct sow | March 20 – April 3 | 4 weeks before |
| Okra | Start indoors | March 20 – April 3 | 4 weeks before |
| Radishes | Direct sow | March 20 – April 3 | 4 weeks before |
| Turnips | Direct sow | March 20 – April 3 | 4 weeks before |
| Cabbage | Set out | March 27 – April 10 | 3 weeks before |
| Carrots | Direct sow | March 27 – April 10 | 3 weeks before |
| Collards | Direct sow | March 27 – April 10 | 3 weeks before |
| Collards | Set out | March 27 – April 10 | 3 weeks before |
| Cucumbers | Start indoors | March 27 – April 10 | 3 weeks before |
| Green Onions | Set out | March 27 – April 10 | 3 weeks before |
| Kale | Direct sow | March 27 – April 10 | 3 weeks before |
| Kale | Set out | March 27 – April 10 | 3 weeks before |
| Kohlrabi | Direct sow | March 27 – April 10 | 3 weeks before |
| Kohlrabi | Set out | March 27 – April 10 | 3 weeks before |
| Leaf Lettuce | Direct sow | March 27 – April 10 | 3 weeks before |
| Pumpkins | Start indoors | March 27 – April 10 | 3 weeks before |
| Summer Squash | Start indoors | March 27 – April 10 | 3 weeks before |
| Winter Squash | Start indoors | March 27 – April 10 | 3 weeks before |
| Zucchini | Start indoors | March 27 – April 10 | 3 weeks before |
| Bok Choy | Direct sow | April 3 – April 17 | 2 weeks before |
| Bok Choy | Set out | April 3 – April 17 | 2 weeks before |
| Broccoli | Set out | April 3 – April 17 | 2 weeks before |
| Cilantro | Direct sow | April 3 – April 17 | 2 weeks before |
| Leaf Lettuce | Set out | April 3 – April 17 | 2 weeks before |
| Swiss Chard | Direct sow | April 3 – April 17 | 2 weeks before |
| Swiss Chard | Set out | April 3 – April 17 | 2 weeks before |
| Dill | Direct sow | April 10 – April 24 | 1 week before |
| Bush Beans | Direct sow | April 24 – May 8 | 1 week after |
| Cucumbers | Set out | April 24 – May 8 | 1 week after |
| Pumpkins | Direct sow | April 24 – May 8 | 1 week after |
| Pumpkins | Set out | April 24 – May 8 | 1 week after |
| Summer Squash | Direct sow | April 24 – May 8 | 1 week after |
| Summer Squash | Set out | April 24 – May 8 | 1 week after |
| Sweet Corn | Direct sow | April 24 – May 8 | 1 week after |
| Tomatoes | Set out | April 24 – May 8 | 1 week after |
| Winter Squash | Direct sow | April 24 – May 8 | 1 week after |
| Winter Squash | Set out | April 24 – May 8 | 1 week after |
| Zucchini | Direct sow | April 24 – May 8 | 1 week after |
| Zucchini | Set out | April 24 – May 8 | 1 week after |
| Cucumbers | Direct sow | May 1 – May 15 | 2 weeks after |
| Okra | Direct sow | May 1 – May 15 | 2 weeks after |
| Okra | Set out | May 1 – May 15 | 2 weeks after |
| Peppers | Set out | May 1 – May 15 | 2 weeks after |
| Southern Peas | Direct sow | May 1 – May 15 | 2 weeks after |
| Sweet Potato | Set out | May 1 – May 15 | 2 weeks after |
The week offsets are conventional extension guidance and vary by variety; the freeze dates they are counted from are measured. For a single date rather than a range, run when do I start my seeds? with your own ZIP code.
What survives the winter changes across Columbus, OH
Of 74 perennial fruits, nuts, berries, vegetables and herbs, 51 come through the winter in every zone this metro covers.
| Zone | ZIPs | Survive | Fail for being too warm |
|---|---|---|---|
| 6a | 58 | 51 of 74 | 0 |
| 6b | 75 | 51 of 74 | 0 |
The last column is the counterintuitive one, and it is why the totals do not simply rise as the winters get milder. Most temperate fruit needs a documented number of hours below about 45 °F to break dormancy and set a crop, so an apple fails in a winter that is too warm; currants and rhubarb cook in the summer heat that comes with it. See the full list with reasons.
Cautious — shortens the seasonMedian across stationsOptimistic
- Last spring freeze
- Plan to May 18 to be careful. Median April 17 – May 1 across 21 stations; April 2 is the optimistic end.
- First fall freeze
- Plan to September 27 to be careful. Median October 10 – October 28 across 21 stations; November 9 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 21 stations behind these numbers
All 21 NOAA stations whose normals this page quotes, spanning about 132 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 metro area.
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.
Every figure above comes from these, and each is named so you can check it. Which station serves a given ZIP code, and how far away it is, varies across the metro — the table below gives it per ZIP code rather than this page averaging it.
| Station | NOAA ID | Last spring freeze | First fall freeze | Season |
|---|---|---|---|---|
| Bellefontaine, OH | USC00330563 | April 26 | October 20 | 175 days |
| Centerburg 2 SE, OH | USC00331404 | April 27 | October 17 | 172 days |
| Circleville, OH | USC00331592 | April 17 | October 28 | 192 days |
| Columbus Ohio State Univ AP, OH | USW00004804 | April 22 | October 23 | 183 days |
| Columbus Port Columbus INTL AP, OH | USW00014821 | April 18 | October 27 | 191 days |
| Columbus Wcmh, OH | USC00331785 | April 20 | October 24 | 185 days |
| Columbus-Valley Crossing, OH | USC00331783 | April 23 | October 19 | 177 days |
| Fredericktown 4 S, OH | USC00332956 | May 1 | October 10 | 161 days |
| Galion Wtr Wks, OH | USC00333021 | April 26 | October 20 | 176 days |
| Lancaster Fairfield AP, OH | USW00053844 | April 26 | October 13 | 169 days |
| Lancaster, OH | USC00334403 | April 22 | October 24 | 183 days |
| Logan, OH | USC00334672 | April 30 | October 14 | 167 days |
| London Fish Hatchery, OH | USC00334681 | April 24 | October 18 | 175 days |
| Marion 2 N, OH | USC00334942 | April 25 | October 20 | 178 days |
| Marion Muni AP, OH | USW00004855 | April 24 | October 20 | 178 days |
| Marysville, OH | USC00334979 | April 19 | October 26 | 188 days |
| New Lexington 2 NW, OH | USC00335857 | April 30 | October 17 | 168 days |
| Newark Heath AP, OH | USW00004858 | April 22 | October 18 | 178 days |
| Newark Wtr Wks, OH | USC00335747 | April 29 | October 16 | 167 days |
| Washington Court House, OH | USC00338794 | April 23 | October 21 | 181 days |
| Westerville, OH | USC00338951 | April 22 | October 24 | 183 days |
These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.
Every ZIP code in Columbus, OH
Zones are published per ZIP code, not per metro area, so this is the exact answer rather than the metro area'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 |
|---|---|---|---|
| 43001 | 6a | Newark Heath AP, OH | 14.8 km |
| 43002 | 6b | Columbus Ohio State Univ AP, OH | 8.0 km |
| 43003 | 6a | Marion Muni AP, OH | 23.9 km |
| 43004 | 6b | Columbus Port Columbus INTL AP, OH | 7.0 km |
| 43007 | 6a | Marysville, OH | 19.0 km |
| 43008 | 6a | Newark Heath AP, OH | 10.1 km |
| 43013 | 6a | Centerburg 2 SE, OH | 7.4 km |
| 43015 | 6b | Marysville, OH | 21.0 km |
| 43016 | 6b | Columbus Ohio State Univ AP, OH | 6.5 km |
| 43017 | 6b | Columbus Ohio State Univ AP, OH | 6.5 km |
| 43018 | 6a | Columbus Port Columbus INTL AP, OH | 17.9 km |
| 43021 | 6b | Westerville, OH | 10.4 km |
| 43023 | 6a | Newark Heath AP, OH | 8.2 km |
| 43025 | 6a | Newark Heath AP, OH | 7.4 km |
| 43026 | 6b | Columbus Ohio State Univ AP, OH | 10.6 km |
| 43027 | 6a | Centerburg 2 SE, OH | 11.9 km |
| 43029 | 6a | Marysville, OH | 18.2 km |
| 43030 | 6a | Newark Heath AP, OH | 7.7 km |
| 43031 | 6a | Centerburg 2 SE, OH | 14.3 km |
| 43032 | 6b | Westerville, OH | 22.5 km |
| 43033 | 6a | Newark Heath AP, OH | 13.5 km |
| 43035 | 6b | Westerville, OH | 7.9 km |
| 43040 | 6a | Marysville, OH | 10.7 km |
| 43045 | 6a | Marysville, OH | 16.5 km |
| 43046 | 6a | Newark Heath AP, OH | 15.0 km |
| 43054 | 6a | Columbus Port Columbus INTL AP, OH | 11.0 km |
| 43055 | 6a | Newark Wtr Wks, OH | 3.9 km |
| 43056 | 6a | Newark Wtr Wks, OH | 11.1 km |
| 43061 | 6b | Marysville, OH | 12.0 km |
| 43062 | 6a | Columbus Port Columbus INTL AP, OH | 16.8 km |
| 43064 | 6b | Marysville, OH | 10.8 km |
| 43065 | 6b | Columbus Ohio State Univ AP, OH | 11.1 km |
| 43066 | 6b | Marion 2 N, OH | 24.0 km |
| 43067 | 6a | Bellefontaine, OH | 24.7 km |
| 43068 | 6b | Columbus Port Columbus INTL AP, OH | 9.1 km |
| 43071 | 6a | Newark Wtr Wks, OH | 11.3 km |
| 43074 | 6a | Centerburg 2 SE, OH | 16.8 km |
| 43076 | 6a | Newark Heath AP, OH | 15.3 km |
| 43077 | 6a | Marysville, OH | 8.9 km |
| 43080 | 6a | Newark Wtr Wks, OH | 17.1 km |
| 43081 | 6b | Westerville, OH | 4.9 km |
| 43082 | 6b | Westerville, OH | 6.0 km |
| 43085 | 6b | Columbus Ohio State Univ AP, OH | 6.1 km |
| 43102 | 6b | Lancaster Fairfield AP, OH | 15.7 km |
| 43103 | 6b | Circleville, OH | 13.7 km |
| 43105 | 6b | Lancaster Fairfield AP, OH | 12.9 km |
| 43107 | 6a | Lancaster, OH | 16.7 km |
| 43109 | 6b | Columbus-Valley Crossing, OH | 7.6 km |
| 43110 | 6b | Columbus-Valley Crossing, OH | 13.4 km |
| 43111 | 6a | Logan, OH | 13.4 km |
| 43112 | 6b | Lancaster Fairfield AP, OH | 5.4 km |
| 43113 | 6b | Circleville, OH | 2.7 km |
| 43116 | 6b | Columbus-Valley Crossing, OH | 19.1 km |
| 43117 | 6b | Circleville, OH | 27.7 km |
| 43119 | 6b | Columbus Wcmh, OH | 17.9 km |
| 43123 | 6b | Columbus-Valley Crossing, OH | 17.3 km |
| 43125 | 6b | Columbus-Valley Crossing, OH | 7.9 km |
| 43127 | 6a | Logan, OH | 8.5 km |
| 43130 | 6a | Lancaster, OH | 2.2 km |
| 43135 | 6b | Circleville, OH | 25.8 km |
| 43136 | 6b | Lancaster Fairfield AP, OH | 14.5 km |
| 43137 | 6b | Columbus-Valley Crossing, OH | 12.1 km |
| 43138 | 6b | Logan, OH | 2.3 km |
| 43140 | 6a | London Fish Hatchery, OH | 7.2 km |
| 43143 | 6b | Washington Court House, OH | 22.8 km |
| 43144 | 6b | Logan, OH | 17.1 km |
| 43145 | 6b | Washington Court House, OH | 14.4 km |
| 43146 | 6b | Columbus-Valley Crossing, OH | 23.6 km |
| 43147 | 6b | Columbus-Valley Crossing, OH | 15.0 km |
| 43148 | 6a | Lancaster, OH | 14.8 km |
| 43149 | 6b | Logan, OH | 15.8 km |
| 43150 | 6a | New Lexington 2 NW, OH | 17.3 km |
| 43151 | 6a | London Fish Hatchery, OH | 18.5 km |
| 43152 | 6b | Logan, OH | 24.5 km |
| 43153 | 6a | London Fish Hatchery, OH | 17.5 km |
| 43154 | 6a | Circleville, OH | 10.8 km |
| 43155 | 6a | Lancaster, OH | 11.6 km |
| 43157 | 6b | Lancaster Fairfield AP, OH | 13.5 km |
| 43158 | 6b | Logan, OH | 9.6 km |
| 43162 | 6b | London Fish Hatchery, OH | 18.1 km |
| 43164 | 6b | Circleville, OH | 14.4 km |
| 43201 | 6b | Columbus Wcmh, OH | 4.4 km |
| 43202 | 6b | Columbus Wcmh, OH | 1.2 km |
| 43203 | 6b | Columbus Wcmh, OH | 7.6 km |
| 43204 | 6b | Columbus Wcmh, OH | 8.6 km |
| 43205 | 6b | Columbus-Valley Crossing, OH | 6.9 km |
| 43206 | 6b | Columbus-Valley Crossing, OH | 6.2 km |
| 43207 | 6b | Columbus-Valley Crossing, OH | 3.9 km |
| 43209 | 6b | Columbus-Valley Crossing, OH | 5.5 km |
| 43210 | 6b | Columbus Wcmh, OH | 2.1 km |
| 43211 | 6b | Columbus Wcmh, OH | 5.0 km |
| 43212 | 6b | Columbus Wcmh, OH | 4.5 km |
| 43213 | 6b | Columbus Port Columbus INTL AP, OH | 2.7 km |
| 43214 | 6b | Columbus Wcmh, OH | 3.1 km |
| 43215 | 6b | Columbus Wcmh, OH | 6.6 km |
| 43217 | 6b | Columbus-Valley Crossing, OH | 9.8 km |
| 43218 | 6b | Columbus Port Columbus INTL AP, OH | 4.7 km |
| 43219 | 6b | Columbus Port Columbus INTL AP, OH | 3.8 km |
| 43220 | 6b | Columbus Ohio State Univ AP, OH | 3.3 km |
| 43221 | 6b | Columbus Wcmh, OH | 4.2 km |
| 43222 | 6b | Columbus Wcmh, OH | 7.1 km |
| 43223 | 6b | Columbus-Valley Crossing, OH | 9.9 km |
| 43224 | 6b | Columbus Wcmh, OH | 5.7 km |
| 43227 | 6b | Columbus-Valley Crossing, OH | 5.1 km |
| 43228 | 6b | Columbus Wcmh, OH | 10.9 km |
| 43229 | 6b | Westerville, OH | 5.4 km |
| 43230 | 6b | Columbus Port Columbus INTL AP, OH | 5.2 km |
| 43231 | 6b | Westerville, OH | 5.3 km |
| 43232 | 6b | Columbus-Valley Crossing, OH | 4.6 km |
| 43235 | 6b | Columbus Ohio State Univ AP, OH | 0.4 km |
| 43240 | 6b | Westerville, OH | 3.9 km |
| 43315 | 6a | Marion Muni AP, OH | 21.7 km |
| 43317 | 6a | Fredericktown 4 S, OH | 14.1 km |
| 43320 | 6a | Marion Muni AP, OH | 14.2 km |
| 43325 | 6a | Galion Wtr Wks, OH | 6.7 km |
| 43334 | 6a | Centerburg 2 SE, OH | 16.9 km |
| 43338 | 6a | Galion Wtr Wks, OH | 18.0 km |
| 43344 | 6a | Marysville, OH | 27.2 km |
| 43358 | 6a | Bellefontaine, OH | 21.2 km |
| 43721 | 6a | Newark Heath AP, OH | 19.1 km |
| 43730 | 6a | New Lexington 2 NW, OH | 14.9 km |
| 43731 | 6a | New Lexington 2 NW, OH | 13.4 km |
| 43739 | 6a | New Lexington 2 NW, OH | 19.8 km |
| 43740 | 6a | Newark Heath AP, OH | 22.4 km |
| 43748 | 6a | New Lexington 2 NW, OH | 9.7 km |
| 43760 | 6a | New Lexington 2 NW, OH | 17.4 km |
| 43761 | 6a | New Lexington 2 NW, OH | 9.2 km |
| 43764 | 6a | New Lexington 2 NW, OH | 3.7 km |
| 43766 | 6a | Logan, OH | 13.8 km |
| 43782 | 6a | New Lexington 2 NW, OH | 12.4 km |
| 43783 | 6a | New Lexington 2 NW, OH | 9.6 km |
| 44833 | 6a | Galion Wtr Wks, OH | 1.5 km |
| 45764 | 6b | Logan, OH | 17.2 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.
Your own ZIP
Work out your own dates
Each of these takes a ZIP code and answers for that ZIP alone, citing the station it used and how far away it is. There is a ZIP box in the header of every page.
-
What survives my winter?
Runs on the hardiness zone, so it answers for all of Columbus, OH at once — zone across 74 perennial fruits, berries, vegetables and herbs.
- When do I start my seeds?
Dates every spring job from your own last freeze — sow indoors, set out, direct sow.
- When do I sow the next round?
How often each crop is worth re-sowing, and when the next sowing is due.
- What can I still plant?
Counts the growing days left before your first fall freeze, crop by crop.
Other places to compare
These metros span exactly the same zones — 6a–6b — so the same plants are in and out of range across them. The freeze dates and the spring calendar are their own.
- Indianapolis-Carmel-Greenwood, IN — zones 6a–6b
- Rochester, NY — zones 6a–6b
- Toledo, OH — zones 6a–6b
- Dayton-Kettering-Beavercreek, OH — zones 6a–6b
- Topeka, KS — zones 6a–6b
- Youngstown-Warren, OH — zones 6a–6b
- Akron, OH — zones 6a–6b
- Johnstown, PA — zones 6a–6b
Gardening in Ohio — zones 6a– 7a covers the whole state: how its 1,212 ZIP codes divide between 3 hardiness zones, and the freeze dates across every NOAA station in it.
Other metro areas in OH:
- Cleveland, OH Zones 6a–7a
- Toledo, OH Zones 6a–6b
- Dayton-Kettering-Beavercreek, OH Zones 6a–6b
- Youngstown-Warren, OH Zones 6a–6b
- Akron, OH Zones 6a–6b
- Canton-Massillon, OH Zones 6a–6b
- Sandusky, OH Zones 6b–7a
- Springfield, OH Zones 6a–6b
- Lima, OH Zone 6a
- Mansfield, OH Zone 6a
- Cincinnati, OH-KY-IN Zones 6a–7a
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 6a 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 6a, 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
The hardiness zone is the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. The freeze dates are NOAA's 1991–2020 Climate Normals, read from every station whose normals cover a ZIP code in this metro. Nothing here is estimated, and no station stands in for another.
This page names no single station on purpose. Picking one to represent a metro sounds reasonable and is not: the station serving the most ZIP codes is an artifact of where ZIP centroids happen to fall, and it selects a lock on the Monongahela for Pittsburgh and a far southern suburb for Chicago. A range across every station is true; a single cited date for a whole metro is not.