In Thunder Bay, the average last spring frost is May 22 and the average first fall frost is Oct 5, a growing season of about 136 days (zone 4a). Start tomatoes indoors around Apr 10 and move them outside from Jun 5. Plant garlic Oct 12 to Oct 19, one to two weeks after the first fall frost.
Thunder Bay at a glance
- Last spring frost
- May 22 (average)
- First fall frost
- Oct 5 (average)
- Frost-free season
- About 136 days
- Hardiness zone
- 4a (NRCan)
- Weather stations
- Grand Portage, MN and Grand Marais, MN (two stations), 1991 to 2020 normals. GrowSmart's dates are the median of these stations, to within 3 days
An average frost date means frost is still possible after it in about half of years. GrowSmart times tender crops like tomatoes, peppers and basil after this date, not on it.
What to plant in Thunder Bay this month (January)
Nothing is scheduled to be sown or planted in Thunder Bay in January. Next up: start onions indoors on Mar 13.
What to plant in Thunder Bay this month (February)
Nothing is scheduled to be sown or planted in Thunder Bay in February. Next up: start onions indoors on Mar 13.
What to plant in Thunder Bay this month (March)
- Start onions indoors: Mar 13
Coming up in early April: start tomatoes indoors (Apr 10), start peppers indoors (Apr 10), start eggplant indoors (Apr 10) and start lettuce indoors (Apr 10).
What to plant in Thunder Bay this month (April)
- Start tomatoes indoors: Apr 10
- Start peppers indoors: Apr 10
- Start eggplant indoors: Apr 10
- Start lettuce indoors: Apr 10
- Start kale indoors: Apr 17
- Start broccoli indoors: Apr 17
- Start cabbage indoors: Apr 17
- Start basil indoors: Apr 24
Coming up in early May: direct sow spinach (May 1), direct sow peas (May 1), direct sow radishes (May 1), transplant lettuce (May 8), direct sow carrots (May 8), start cucumbers indoors (May 8), start zucchini indoors (May 8) and start winter squash indoors (May 8).
What to plant in Thunder Bay this month (May)
- Direct sow spinach: May 1
- Direct sow peas: May 1
- Direct sow radishes: May 1
- Transplant lettuce: May 8
- Direct sow carrots: May 8
- Start cucumbers indoors: May 8
- Start zucchini indoors: May 8
- Start winter squash indoors: May 8
- Direct sow beets: May 15
- Transplant kale: May 15
- Transplant broccoli: May 15
- Transplant cabbage: May 15
- Direct sow potatoes: May 15
- Transplant onions: May 22
- Transplant cucumbers: May 29
- Transplant zucchini: May 29
- Transplant winter squash: May 29
- Direct sow beans: May 29
Coming up in early June: transplant tomatoes (Jun 5), transplant peppers (Jun 5), transplant eggplant (Jun 5) and transplant basil (Jun 5).
What to plant in Thunder Bay this month (June)
- Transplant tomatoes: Jun 5
- Transplant peppers: Jun 5
- Transplant eggplant: Jun 5
- Transplant basil: Jun 5
What to plant in Thunder Bay this month (July)
- Sow peas for a fall harvest: Jul 27
- Sow kale for a fall harvest: Jul 27
Coming up in early August: sow lettuce for a fall harvest (Aug 10).
What to plant in Thunder Bay this month (August)
- Sow lettuce for a fall harvest: Aug 10
- Sow spinach for a fall harvest: Aug 17
- Sow radishes for a fall harvest: Aug 31
What to plant in Thunder Bay this month (September)
Nothing is scheduled to be sown or planted in Thunder Bay in September. Next up: plant garlic on Oct 12.
What to plant in Thunder Bay this month (October)
- Plant garlic: Oct 12 to Oct 19
What to plant in Thunder Bay this month (November)
Nothing is scheduled to be sown or planted in Thunder Bay in November. Next up: start onions indoors on Mar 13.
What to plant in Thunder Bay this month (December)
Nothing is scheduled to be sown or planted in Thunder Bay in December. Next up: start onions indoors on Mar 13.
Thunder Bay planting calendar
| Crop | Start indoors | Plant outside | Harvest |
|---|---|---|---|
| Tomatoes | Apr 10 | Transplant Jun 5 | From Aug 22 |
| Peppers | Apr 10 | Transplant Jun 5 | From Aug 16 |
| Eggplant | Apr 10 | Transplant Jun 5 | From Aug 19 |
| Basil | Apr 24 | Transplant Jun 5 | From Jul 17 |
| Onions (from seed) | Mar 13 | Transplant May 22 | From Aug 30 |
| Lettuce | Apr 10 | Transplant May 8Fall: direct sow Aug 10 | From Jun 17Fall: from Sep 19 |
| Spinach | n/a | Direct sow May 1Fall: direct sow Aug 17 | From Jun 10Fall: from Sep 26 |
| Peas | n/a | Direct sow May 1Fall: direct sow Jul 27 | From Jun 30Fall: from Sep 25 |
| Radishes | n/a | Direct sow May 1Fall: direct sow Aug 31 | From May 26Fall: from Sep 25 |
| Carrots | n/a | Direct sow May 8 | From Jul 17 |
| Beets | n/a | Direct sow May 15 | From Jul 9 |
| Kale | Apr 17 | Transplant May 15Fall: direct sow Jul 27 | From Jul 9Fall: from Sep 20 |
| Broccoli | Apr 17 | Transplant May 15 | From Jul 19 |
| Cabbage | Apr 17 | Transplant May 15 | From Jul 24 |
| Cucumbers | May 8 | Transplant May 29 | From Jul 23 |
| Zucchini | May 8 | Transplant May 29 | From Jul 18 |
| Winter squash | May 8 | Transplant May 29 | From Aug 27 |
| Beans | n/a | Direct sow May 29 | From Jul 23 |
| Potatoes | n/a | Direct sow May 15 | From Aug 3 |
| Garlic | n/a | Plant cloves Oct 12 to Oct 19 | Around Aug 14 the next year |
Dates are for one planting of each crop, from Thunder Bay's average frost dates. Tomatoes are indeterminate, lettuce is looseleaf and beans are bush beans. Harvest dates are when the first picking is usually ready. Garlic follows University of Minnesota Extension (see below).
Fall planting in Thunder Bay
Plant garlic Oct 12 to Oct 19. That is one to two weeks after Thunder Bay's average first fall frost of Oct 5, the timing University of Minnesota Extension recommends, so the cloves root before winter without sending shoots up. Harvest comes around Aug 14 the following summer. How to plant garlic in Thunder Bay.
Shallots: GrowSmart's plan has you plant shallot sets in fall in zone 5 and warmer, and in spring in colder zones.
Cool-season crops GrowSmart schedules for a fall harvest in Thunder Bay:
- Peas: sow Jul 27, ready from about Sep 25
- Kale: sow Jul 27, ready from about Sep 20
- Lettuce: sow Aug 10, ready from about Sep 19
- Spinach: sow Aug 17, ready from about Sep 26
- Radishes: sow Aug 31, ready from about Sep 25
Nearby planting calendars
Thunder Bay planting questions
When is the last frost in Thunder Bay?
The average last spring frost in Thunder Bay is May 22, and the average first fall frost is Oct 5, from 1991 to 2020 climate normals at 3 nearby weather stations. Frost is still possible after the spring date in about half of years.
When should I start tomato seeds in Thunder Bay?
Start tomatoes indoors around Apr 10, 8 weeks before moving them outside around Jun 5, which is two weeks after the average last frost.
What can I plant in Thunder Bay in fall?
Garlic goes in Oct 12 to Oct 19. For fall harvests, sow peas and kale around Jul 27, lettuce around Aug 10, spinach around Aug 17 and radishes around Aug 31.