Plymouth, Minnesota: planting zone & frost dates
Plymouth is in USDA plant hardiness zone 5a, where the average coldest winter night reaches -20 to -15°F (-28.9 to -26.1°C). The typical last spring frost is around May 4 and the first fall frost around Oct 5.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 12 | Sep 29 |
| Typical planning date (30% risk) | May 4 | Oct 5 |
| Median (50%) | Apr 29 | Oct 12 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station NEW HOPE, MN (USC00215838), 4.2 mi (6.7 km) from the city center and 46 ft lower than the city center (-14 m). Record used for the 1991–2020 normals: 27 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Plymouth
All 4 ZIP codes covering Plymouth are in zone 5a.
Vegetable planting calendar for Plymouth
Dates are counted from the 30%-risk frost dates above (last frost May 4, first frost Oct 5). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 9 – Mar 23 | May 11 – May 25 | — | — |
| Pepper | Feb 23 – Mar 9 | May 18 – Jun 1 | — | — |
| Lettuce | Mar 23 – Apr 6 | Apr 20 – May 11 | Apr 6 – May 18 | Jul 27 – Aug 24 |
| Green Beans | — | — | May 11 – Jun 15 | Jul 13 – Jul 27 |
| Sweet Corn | — | — | May 11 – Jun 8 | — |
| Zucchini & Summer Squash | Apr 6 – Apr 13 | May 11 – May 25 | May 11 – Jun 1 | Jul 13 – Jul 27 |
| Cucumber | Apr 6 – Apr 13 | May 18 – May 25 | May 11 – Jun 1 | Jul 13 – Jul 27 |
| Carrot | — | — | Apr 13 – May 18 | Jul 13 – Jul 27 |
| Onion | Feb 9 – Feb 23 | Apr 6 – Apr 20 | — | — |
| Potato | — | Apr 6 – Apr 27 | — | — |
| Basil | Mar 23 – Apr 6 | May 18 – Jun 1 | May 18 – Jun 8 | — |
| Spinach | — | — | Mar 23 – Apr 20 | Aug 10 – Sep 7 |
| Kale | Mar 9 – Mar 23 | Apr 6 – Apr 27 | Apr 6 – Apr 27 | Jul 27 – Aug 24 |
| Broccoli | Mar 9 – Mar 23 | Apr 20 – May 11 | — | Jul 13 – Jul 27 |
| Peas | — | — | Mar 23 – Apr 13 | Jul 27 – Aug 10 |
| Eggplant | Feb 23 – Mar 9 | May 18 – Jun 1 | — | — |
| Cabbage | Mar 9 – Mar 23 | Apr 6 – Apr 20 | — | Jul 13 – Jul 27 |
| Radish | — | — | Mar 30 – May 18 | Aug 24 – Sep 21 |
| Strawberry | — | Apr 6 – Apr 27 | — | — |
| Beets | — | — | Apr 13 – May 25 | Jul 27 – Aug 10 |
Nearby cities in Minnesota
- Brooklyn Park — zone 5a, last frost May 6, first frost Oct 2
- Minneapolis — zone 5a, last frost Apr 30, first frost Oct 10
- Bloomington — zone 5a, last frost Apr 30, first frost Oct 11
- St. Paul — zone 5a, last frost May 1, first frost Oct 7
- Lakeville — zone 4b, last frost May 2, first frost Oct 4
- Woodbury — zone 5a, last frost May 1, first frost Oct 5
More: all Minnesota cities · other zone 5a cities: Minneapolis, MN, St. Paul, MN, Anchorage, AK, Sioux Falls, SD, Cedar Rapids, IA, Billings, MT, Bloomington, MN, Sioux City, IA
Plymouth gardening questions
When is the last frost in Plymouth, MN?
Plan around May 4. At NOAA's NEW Hope, MN station, 4.2 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by Apr 29, and after May 12 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 19. The last frost is fairly predictable here: only 27 days separate the 90% and 10% dates (median for cities on this site: 36 days).
When should I plant tomatoes in Plymouth, MN?
Start seeds indoors Mar 9 – Mar 23 and set transplants outside May 11 – May 25, once nights stay above 50°F and the soil is near 60°F. That leaves 154 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Plymouth?
About 163 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 144 days, and in 1 year in 10 it runs 182 days or more. In fall there is a 10% chance of frost by Sep 29 and a 30% chance by Oct 5. That ranks 6th longest of 9 Minnesota cities on this site.
When should I plant a fall garden in Plymouth?
Count back from the first fall frost (Oct 5): transplant broccoli Jul 13 – Jul 27; sow kale Jul 27 – Aug 24; sow lettuce Jul 27 – Aug 24; sow radishes Aug 24 – Sep 21. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 22. How the math works: succession and fall planting.
Did Plymouth's hardiness zone change on the 2023 map?
Yes. Most of Plymouth was zone 4b on the 2012 map and is zone 5a on the 2023 map — half a zone warmer, like about 56% of U.S. ZIP codes. The shift comes from a newer 1991–2020 averaging period plus more weather stations and better mapping; it does not mean last frost comes earlier. Why the 2023 map is warmer.
How does Plymouth compare with Brooklyn Park, MN?
Both are in zone 5a. The typical last spring frost in Plymouth (May 4) comes about the same time as in Brooklyn Park, MN (May 6), 8 miles away, and the first fall frost is Oct 5 versus Oct 2. The two cities use different NOAA stations.