Place guide
Planting zones in Helena, MT
This metro spans USDA zones 4b to 5a, so there is no single zone for Helena, MT and anyone who gives you one is rounding. 58% of its ZIP codes are zone 4b; the rest are not.
Your ZIP code
Get the exact answer for your address
Everything above describes Helena, MT 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 Helena, MT is closing
Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives September 5 – September 30 across the 9 NOAA stations serving this metro area .
Your next season already has a date
The first job of it is 🧅 Green Onions, start indoors, around March 14 – April 23 — counted back from a last spring freeze of May 9 – June 18 here.
These are ranges across the whole metro area. The ZIP lookup above gives the dates from your own nearest station instead.
All 9 stations agreeAt least one station
Every one of the 9 NOAA stations serving this metro area counts June 18 – September 5 as growing season (79 days). Widening to any single station gives May 9 – September 30 (144 days).
That is a 65-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
Helena, MT 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 58% in zone 4b and wrong for the other 42%. Here is the actual split.
| Zone | ZIP codes | Share | |
|---|---|---|---|
| 4b | 11 | 58% | |
| 5a | 8 | 42% |
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 9 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 9 stations serving Helena, MT it runs 81–142 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 75–82 °F , below the 90 °F point where cool-season crops reliably bolt. Summer rain over the same months runs 4.3–5.8" across those 9 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 38% 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 78 °F summer afternoon drying the soil faster than a cool one.
When to start seeds in Helena, MT
Every spring job for 63 crop dates, counted from this metro's own last spring freeze. Each is a range across all 9 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 | March 14 – April 23 | 8 weeks before |
| Peppers | Start indoors | March 14 – April 23 | 8 weeks before |
| Broccoli | Start indoors | March 28 – May 7 | 6 weeks before |
| Cabbage | Start indoors | March 28 – May 7 | 6 weeks before |
| Collards | Start indoors | March 28 – May 7 | 6 weeks before |
| Kale | Start indoors | March 28 – May 7 | 6 weeks before |
| Leaf Lettuce | Start indoors | March 28 – May 7 | 6 weeks before |
| Peas | Direct sow | March 28 – May 7 | 6 weeks before |
| Spinach | Direct sow | March 28 – May 7 | 6 weeks before |
| Sweet Potato | Start indoors | March 28 – May 7 | 6 weeks before |
| Tomatoes | Start indoors | March 28 – May 7 | 6 weeks before |
| Bok Choy | Start indoors | April 4 – May 14 | 5 weeks before |
| Kohlrabi | Start indoors | April 4 – May 14 | 5 weeks before |
| Swiss Chard | Start indoors | April 4 – May 14 | 5 weeks before |
| Arugula | Direct sow | April 11 – May 21 | 4 weeks before |
| Baby Salad Greens | Direct sow | April 11 – May 21 | 4 weeks before |
| Beets | Direct sow | April 11 – May 21 | 4 weeks before |
| Green Onions | Direct sow | April 11 – May 21 | 4 weeks before |
| Mustard Greens | Direct sow | April 11 – May 21 | 4 weeks before |
| Okra | Start indoors | April 11 – May 21 | 4 weeks before |
| Radishes | Direct sow | April 11 – May 21 | 4 weeks before |
| Turnips | Direct sow | April 11 – May 21 | 4 weeks before |
| Cabbage | Set out | April 18 – May 28 | 3 weeks before |
| Carrots | Direct sow | April 18 – May 28 | 3 weeks before |
| Collards | Direct sow | April 18 – May 28 | 3 weeks before |
| Collards | Set out | April 18 – May 28 | 3 weeks before |
| Cucumbers | Start indoors | April 18 – May 28 | 3 weeks before |
| Green Onions | Set out | April 18 – May 28 | 3 weeks before |
| Kale | Direct sow | April 18 – May 28 | 3 weeks before |
| Kale | Set out | April 18 – May 28 | 3 weeks before |
| Kohlrabi | Direct sow | April 18 – May 28 | 3 weeks before |
| Kohlrabi | Set out | April 18 – May 28 | 3 weeks before |
| Leaf Lettuce | Direct sow | April 18 – May 28 | 3 weeks before |
| Pumpkins | Start indoors | April 18 – May 28 | 3 weeks before |
| Summer Squash | Start indoors | April 18 – May 28 | 3 weeks before |
| Winter Squash | Start indoors | April 18 – May 28 | 3 weeks before |
| Zucchini | Start indoors | April 18 – May 28 | 3 weeks before |
| Bok Choy | Direct sow | April 25 – June 4 | 2 weeks before |
| Bok Choy | Set out | April 25 – June 4 | 2 weeks before |
| Broccoli | Set out | April 25 – June 4 | 2 weeks before |
| Cilantro | Direct sow | April 25 – June 4 | 2 weeks before |
| Leaf Lettuce | Set out | April 25 – June 4 | 2 weeks before |
| Swiss Chard | Direct sow | April 25 – June 4 | 2 weeks before |
| Swiss Chard | Set out | April 25 – June 4 | 2 weeks before |
| Dill | Direct sow | May 2 – June 11 | 1 week before |
| Bush Beans | Direct sow | May 16 – June 25 | 1 week after |
| Cucumbers | Set out | May 16 – June 25 | 1 week after |
| Pumpkins | Direct sow | May 16 – June 25 | 1 week after |
| Pumpkins | Set out | May 16 – June 25 | 1 week after |
| Summer Squash | Direct sow | May 16 – June 25 | 1 week after |
| Summer Squash | Set out | May 16 – June 25 | 1 week after |
| Sweet Corn | Direct sow | May 16 – June 25 | 1 week after |
| Tomatoes | Set out | May 16 – June 25 | 1 week after |
| Winter Squash | Direct sow | May 16 – June 25 | 1 week after |
| Winter Squash | Set out | May 16 – June 25 | 1 week after |
| Zucchini | Direct sow | May 16 – June 25 | 1 week after |
| Zucchini | Set out | May 16 – June 25 | 1 week after |
| Cucumbers | Direct sow | May 23 – July 2 | 2 weeks after |
| Okra | Direct sow | May 23 – July 2 | 2 weeks after |
| Okra | Set out | May 23 – July 2 | 2 weeks after |
| Peppers | Set out | May 23 – July 2 | 2 weeks after |
| Southern Peas | Direct sow | May 23 – July 2 | 2 weeks after |
| Sweet Potato | Set out | May 23 – July 2 | 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 Helena, MT
Of 74 perennial fruits, nuts, berries, vegetables and herbs, 48 come through the winter in zone 5a and only 34 in zone 4b. That is a different garden at each end of the same metro.
| Zone | ZIPs | Survive | Fail for being too warm |
|---|---|---|---|
| 4b | 11 | 34 of 74 | 0 |
| 5a | 8 | 48 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 July 5 to be careful. Median May 9 – June 18 across 9 stations; April 29 is the optimistic end.
- First fall freeze
- Plan to August 21 to be careful. Median September 5 – September 30 across 9 stations; October 11 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 9 stations behind these numbers
All 9 NOAA stations whose normals this page quotes, spanning about 184 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 |
|---|---|---|---|---|
| Austin 1 W, MT | USC00240375 | June 4 | September 14 | 100 days |
| Boulder, MT | USC00241008 | June 7 | September 8 | 90 days |
| Butte Bert Mooney AP, MT | USW00024135 | June 13 | September 5 | 83 days |
| Gibson Dam, MT | USC00243489 | June 12 | September 8 | 88 days |
| Helena Rgnl AP, MT | USW00024144 | May 9 | September 30 | 142 days |
| Rogers Pass 9 Nne, MT | USC00247159 | May 21 | September 15 | 115 days |
| Tizer Gardens, MT | USC00248239 | June 18 | September 5 | 81 days |
| Townsend 3Se, MT | USC00248324 | May 19 | September 19 | 122 days |
| Trident, MT | USC00248363 | May 9 | September 27 | 139 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 Helena, MT
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 |
|---|---|---|---|
| 59410 | 4b | Gibson Dam, MT | 13.5 km |
| 59601 | 4b | Austin 1 W, MT | 13.7 km |
| 59602 | 4b | Helena Rgnl AP, MT | 14.1 km |
| 59623 | 5a | Helena Rgnl AP, MT | 6.1 km |
| 59631 | 5a | Boulder, MT | 22.2 km |
| 59632 | 5a | Boulder, MT | 10.9 km |
| 59633 | 4b | Austin 1 W, MT | 20.1 km |
| 59634 | 4b | Tizer Gardens, MT | 8.0 km |
| 59635 | 5a | Helena Rgnl AP, MT | 12.7 km |
| 59636 | 4b | Helena Rgnl AP, MT | 11.5 km |
| 59638 | 4b | Tizer Gardens, MT | 1.7 km |
| 59639 | 4b | Rogers Pass 9 Nne, MT | 34.6 km |
| 59640 | 4b | Austin 1 W, MT | 15.7 km |
| 59643 | 5a | Townsend 3Se, MT | 20.7 km |
| 59644 | 4b | Townsend 3Se, MT | 13.1 km |
| 59647 | 5a | Townsend 3Se, MT | 23.9 km |
| 59648 | 4b | Rogers Pass 9 Nne, MT | 12.7 km |
| 59721 | 5a | Trident, MT | 31.8 km |
| 59759 | 5a | Butte Bert Mooney AP, MT | 29.1 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 Helena, MT 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 — 4b–5a — so the same plants are in and out of range across them. The freeze dates and the spring calendar are their own.
- Mankato, MN — zones 4b–5a
- Wausau, WI — zones 4b–5a
- Bozeman, MT — zones 4b–5a
- Sioux Falls, SD-MN — zones 4b–5a
- Bangor, ME — zones 4b–5a
- Rochester, MN — zones 4b–5a
- Billings, MT — zones 4b–5a
- La Crosse-Onalaska, WI-MN — zones 4b–5a
Gardening in Montana — zones 3b– 6b covers the whole state: how its 368 ZIP codes divide between 7 hardiness zones, and the freeze dates across every NOAA station in it.
Other metro areas in MT:
- Great Falls, MT Zones 4a–4b
- Bozeman, MT Zones 4b–5a
- Billings, MT Zones 4b–5a
- Missoula, MT Zones 5a–6a
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 4b 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 4b, 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.