Thunder Bay, ON — Planting Guide
Thunder Bay is in USDA Zone 4b. The average last spring frost is May 7 and the first fall frost is October 1, giving you a growing season of approximately 147 days.
At an elevation of 652 ft, Thunder Bay receives approximately 20.5 in of rainfall annually. Summer highs average 72°F with winter lows around 9°F. The predominant soil type is Clay Loam.
🌡️ Zone
4b (-25°F to -20°F min)
❄️ Last Frost
May 7
🍂 First Frost
October 1
📅 Growing Season
147 days
⛰️ Elevation
652 ft
🌧️ Annual Rainfall
20.5 in
Monthly Watering Calendar
When you'll need to water your garden — based on average monthly rainfall vs. the ~1 inch/week most gardens need.
View detailed monthly data
| Month | Avg Rainfall | Rainy Days | Extra Water Needed | Watering Effort |
|---|---|---|---|---|
| Jan | 0.9 in | 8 days | — | None |
| Feb | 1 in | 6 days | — | None |
| Mar | 1.2 in | 10 days | — | None |
| Apr | 1.8 in | 9 days | 2.5 in | High |
| May | 2.6 in | 10 days | 1.7 in | High |
| Jun | 2.9 in | 9 days | 1.4 in | Moderate |
| Jul | 2.5 in | 10 days | 1.8 in | High |
| Aug | 2 in | 8 days | 2.3 in | High |
| Sep | 1.6 in | 7 days | 2.7 in | High |
| Oct | 1.5 in | 8 days | 2.8 in | High |
| Nov | 1.3 in | 7 days | — | None |
| Dec | 1.2 in | 7 days | — | None |
Annual total: 20.5 in. Water needs vary by crop — tomatoes need ~1.2"/week while herbs like rosemary need only 0.3"/week. Check individual plant pages for crop-specific water budgets that factor in your county's rainfall and soil drainage.
Thunder Bay Soil Profile
Soil Type
Clay Loam
Soil pH
6.0-7.0
Drainage
Well Drained
Gardening Difficulty Score
Thunder Bay is a very forgiving place to garden. Most plants thrive here with minimal effort.
Local Gardening Help in Thunder Bay
Free expert help is closer than you think. Your county's cooperative extension office connects you with trained gardeners, soil testing labs, and local programs — all specific to Thunder Bay's climate and soil.
County Extension Office
Thunder Bay Extension Office
Extension offices are run by land-grant universities and funded by the USDA. Their advice is free, research-based, and tailored to your county's specific conditions.
Master Gardener Program
Free gardening help from trained volunteers
Master Gardeners are community volunteers who complete 40–60 hours of university horticultural training. They answer gardening questions, diagnose plant problems, and offer workshops — all free.
Many extension offices run a Master Gardener hotline where you can call or email with photos of plant problems for free diagnosis.
Soil Testing
Available through your extension office
Before amending your soil, get it tested. Your extension office offers soil testing (typically $10–$25) that tells you exact pH, nutrient levels, and amendment recommendations specific to what you want to grow.
Services Available in Thunder Bay
Finding local nurseries & garden centers in Thunder Bay
Why Buy Local
Local nurseries carry plants that are proven to grow in your area. Staff can give you advice specific to Thunder Bay's soil and climate that big-box stores can't. Plants from local growers are typically hardier because they're already acclimated to your zone.
How to Find Them
Search for "nurseries near Thunder Bay ON" or "garden center Thunder Bay" on Google Maps. Also check with your extension office — they often maintain lists of reputable local nurseries and plant sales.
Community gardens & gardening groups
Community gardens are a great way to learn from experienced gardeners in your area, especially if you're limited on space. Search "community garden Thunder Bay ON" or check your extension office and local parks department. Facebook groups like "Thunder Bay Gardeners" or "Ontario Gardening" are also excellent for local advice and plant swaps.
What to Plant After Your Harvest
After your first crops finish, use the remaining frost-free days to grow a second round.
Show 6 more succession options
Sunlight & Day Length
Monthly daylight hours and peak sun — critical for onion varieties, photoperiod-sensitive plants, and solar garden planning.
Longest Day
15.9 hours
Summer solstice daylight
Shortest Day
8.1 hours
Winter solstice daylight
Peak Sun Hours
10.2 hr/day peak (summer)
Peak sun hours (green dashed line below) account for cloud cover — this is the usable direct sunlight your garden actually receives. Most vegetables need 6+ peak sun hours.
Onion tip: Your long summer days (14+ hours) support long-day onion varieties like Walla Walla, Sweet Spanish, and Ailsa Craig.
View detailed monthly data
| Month | Daylight Hours | Peak Sun Hours | Day Length |
|---|---|---|---|
| January | 8.5 hr | 3.4 hr | Short day |
| February | 9.9 hr | 4.4 hr | Short day |
| March | 11.6 hr | 5.8 hr | Short day |
| April | 13.4 hr | 6.8 hr | Neutral |
| May | 15 hr | 8.3 hr | Long day |
| June | 15.9 hr | 10.2 hr | Long day |
| July | 15.5 hr | 9.7 hr | Long day |
| August | 14.1 hr | 8.7 hr | Long day |
| September | 12.3 hr | 7.3 hr | Neutral |
| October | 10.5 hr | 5.4 hr | Short day |
| November | 8.9 hr | 3.7 hr | Short day |
| December | 8.1 hr | 3 hr | Short day |
Peak sun hours factor in typical cloud cover — use these for solar panel and shade-planning calculations.
Soil Temperature & Composting Calendar
Monthly soil temps tell you when to plant warm-season crops, and when your compost pile is actively working.
Plant Warm Crops When
Soil reaches 60°F+
Soil warm enough from Jun through Sep.
Best Month to Compost
Jun
Microbial activity peaks when soil is warm.
Active Composting
6 months
Solid season. Piles go dormant in winter.
View detailed monthly data
| Month | Soil 4" Deep | Soil 8" Deep | Compost Activity | Time to Finish |
|---|---|---|---|---|
| Jan | 14°F | 23°F | ❄️ Dormant | ~36 weeks |
| Feb | 17°F | 22°F | ❄️ Dormant | ~36 weeks |
| Mar | 24°F | 29°F | ❄️ Dormant | ~36 weeks |
| Apr | 39°F | 39°F | ❄️ Dormant | ~36 weeks |
| May | 55°F | 49°F | ♻️ Active | ~14 weeks |
| Jun | 66°F | 58°F | 🔥 Peak | ~8 weeks |
| Jul | 73°F | 67°F | 🔥 Peak | ~8 weeks |
| Aug | 72°F | 67°F | 🔥 Peak | ~8 weeks |
| Sep | 64°F | 63°F | ♻️ Active | ~14 weeks |
| Oct | 51°F | 56°F | ♻️ Active | ~14 weeks |
| Nov | 35°F | 42°F | ❄️ Dormant | ~36 weeks |
| Dec | 22°F | 30°F | ❄️ Dormant | ~36 weeks |
Highlighted rows = soil 60°F+ (safe for warm-season transplants). Compost finishes fastest during peak activity months.
Pest & Disease Pressure in Thunder Bay
Computed from local climate patterns — warmer, humid conditions increase pest generations and fungal disease risk.
Insect Pest Pressure
Moderate — common pests appear but manageable with monitoring.
Disease Risk
Low disease risk — dry conditions reduce fungal problems.
Seasonal Risk
View 5 common pests in your area
| Pest | Risk Level | Peak Months |
|---|---|---|
| Aphids | Moderate | May, Jun, Jul, Aug |
| Cabbage worms | Low | Jun, Jul, Aug |
| Colorado potato beetle | Low | Jun, Jul |
| Flea beetles | Moderate | May, Jun, Jul |
| Slugs | Low | May, Jun, Jul, Aug, Sep |
Organic pest management tips
- Maintain healthy soil with regular compost additions to build natural pest resistance
- Practice crop rotation annually to break pest cycles
- Encourage beneficial insects with flowering herbs like dill, fennel, and yarrow
Cover Crops for Thunder Bay
Cover crops protect bare soil, fix nitrogen, suppress weeds, and improve soil structure — with county-specific planting dates.
Spring Cover Crops (2 options) — Build soil before the main growing season
| Crop | Plant By | Terminate | N-Fixing | Soil Benefit |
|---|---|---|---|---|
| Buckwheat | May 12 | Aug 6 | — | Rapid growth, attracts pollinators, suppresses weeds |
| White clover | Apr 9 | Aug 6 | ✓ Yes | Living mulch, fixes nitrogen, permanent ground cover |
Summer Cover Crops (1 options) — Fill gaps and suppress weeds between plantings
| Crop | Plant By | Terminate | N-Fixing | Soil Benefit |
|---|---|---|---|---|
| Sunflowers | May 21 | Sep 17 | — | Deep roots break compaction, attract pollinators and beneficial insects |
Fall Cover Crops (5 options) — Plant after harvest to protect soil over winter
| Crop | Plant By | Terminate | N-Fixing | Soil Benefit |
|---|---|---|---|---|
| Daikon radish | Aug 23 | Apr 16 | — | Deep taproot breaks compaction, excellent for clay soils |
| Hairy vetch | Jul 22 | Apr 16 | ✓ Yes | Excellent nitrogen fixer, good for depleted soils |
| Oats | Aug 23 | Apr 16 | — | Quick biomass, winterkills in cold zones — no spring tillage needed |
| Winter rye | Jun 27 | Apr 16 | — | Suppresses weeds, prevents erosion, breaks up compacted soil |
| Winter wheat | Jul 10 | Apr 16 | — | Erosion control, weed suppression, good biomass |
Wind & Microclimate
Wind dries soil, stresses plants, and affects frost patterns. Understanding your exposure helps with garden placement.
Seasonal Wind Speed
Spring: 12 mph Summer: 9 mph
Fall: 11 mph Winter: 12 mph
Prevailing wind: SW. Moderate wind — consider a temporary windbreak for young seedlings.
Windbreak Benefit
6.5/10
Moderately beneficial — a simple fence or trellis can protect delicate crops from wind stress.
Frost Pocket Risk
Low
Relatively flat terrain (275 ft range). Frost pocket risk is minimal — garden placement is flexible.
Rainwater Harvesting Potential
How much water you can collect, when to collect it, and what size system you need for your garden.
Annual Collection
10,217 gal
Per 1,000 sq ft of roof area (at 80% collection efficiency)
Recommended Setup
7 rain barrels (55 gal each)
For a typical 500 sq ft garden. Serious collectors: consider a 1,000 gal tank.
Legal Status
Unrestricted
Rainwater harvesting is fully legal in your state with no restrictions.
Best Collection Months
May, Jun, Jul, Aug
Highest rainfall months — your barrels will fill up quickly during these months.
Months to Draw From Storage
Jan
Dry months when you'll rely on stored water — size your storage for this gap.
Rainwater collection tips for your area
- Your county receives approximately 20.5 inches of rain per year
- A 1,000 sq ft roof can collect roughly 10,217 gallons annually
- Rainwater harvesting is fully legal in your state
- Use a first-flush diverter to keep roof debris out of your collection
Soil & Growing Conditions in Thunder Bay
Soil Type
Clay Loam
Retains moisture well but slow to warm in spring. Amend with compost to improve drainage.
Watering Needs
With 20.5 inches annually, regular irrigation is essential. Drip systems and heavy mulching conserve water.
Season Tips
147-day frost-free season
Start warm-season crops indoors and focus on short-season varieties. Cold frames extend your season by 3–4 weeks in fall.
Free Garden Planner
Plan your entire garden season — organize planting dates, track what you're growing, and know exactly when to start seeds, transplant, and harvest.
Recommended for Your Garden
Cedar raised bed kit — ideal for poor soil, clay, or small-space gardening.
Improve drainage and aeration in heavy clay soils with horticultural perlite.
Premium blend of topsoil, compost, and perlite formulated for raised beds.
🥬 Vegetables to Grow in Thunder Bay
96 vegetables that grow well in Zone 4b with planting dates for Thunder Bay.
Show all 96 vegetables with planting dates
| Plant | Start Indoors | Direct Sow | Transplant | Harvest | Days to Maturity |
|---|---|---|---|---|---|
| Acorn Squash | Mar 26 | May 21 | May 28 | Aug 20 – Sep 24 | 80–100 |
| Amaranth | Mar 5 | May 21 | May 28 | Aug 27 – Oct 15 | 90–120 |
| Arugula | Mar 26 | Apr 30 | May 7 | Jun 11 – Aug 13 | 30–50 |
| Asparagus | — | — | May 21 | — | 730–1095 |
| Beets | — | Apr 30 | — | Jun 25 – Jul 23 | 50–70 |
| Belgian Endive | Mar 26 | Apr 30 | May 7 | Aug 27 – Oct 1 | 110–150 |
| Black Beans | — | May 21 | — | Aug 20 – Oct 8 | 90–120 |
| Bok Choy | Mar 26 | Apr 30 | May 7 | Jun 18 – Jul 23 | 40–60 |
| Broccoli | Mar 26 | Apr 30 | May 7 | Jul 9 – Aug 20 | 60–90 |
| Broccoli Rabe | Mar 26 | Apr 30 | May 7 | Jun 18 – Jul 23 | 40–60 |
| Brussels Sprouts | Mar 26 | Apr 30 | May 7 | Aug 6 – Oct 1 | 90–130 |
| Butternut Squash | Mar 26 | May 21 | May 28 | Aug 27 – Oct 1 | 85–110 |
| Cabbage | Mar 26 | Apr 30 | May 7 | Jul 9 – Sep 3 | 60–100 |
| Carrots | — | Apr 30 | — | Jul 2 – Aug 6 | 60–80 |
| Cauliflower | Mar 26 | Apr 30 | May 7 | Jul 2 – Sep 3 | 55–100 |
| Celeriac | Mar 26 | Apr 30 | May 7 | Aug 20 – Sep 24 | 100–120 |
| Celery | Mar 26 | Apr 30 | May 7 | Jul 30 – Sep 24 | 80–120 |
| Celtuce | Mar 26 | Apr 30 | May 7 | Jul 9 – Aug 20 | 60–90 |
| Chard | Mar 26 | Apr 30 | May 7 | Jul 2 – Aug 20 | 50–60 |
| Chickpeas | Mar 26 | Apr 30 | May 7 | Jul 30 – Sep 10 | 80–110 |
| Chicory | Mar 26 | Apr 30 | May 7 | Jul 9 – Aug 20 | 60–85 |
| Chinese Cabbage | Mar 26 | Apr 30 | May 7 | Jul 2 – Jul 30 | 50–70 |
| Christmas Lima Beans | Mar 5 | May 21 | May 28 | Aug 20 – Sep 24 | 80–100 |
| Collard Greens | Mar 26 | Apr 30 | May 7 | Jul 2 – Sep 3 | 55–75 |
| Corn | — | May 21 | — | Jul 23 – Sep 17 | 60–100 |
| Cress | Mar 26 | Apr 30 | May 7 | May 21 – Jun 11 | 14–21 |
| Crookneck Squash | Mar 26 | May 21 | May 28 | Jul 16 – Aug 13 | 45–60 |
| Crosne | — | Apr 30 | — | Oct 1 – Sep 24 | 150–200 |
| Cucumber | Mar 26 | May 21 | May 28 | Jul 23 – Sep 17 | 50–70 |
| Daikon | — | Apr 30 | — | Jun 25 – Jul 23 | 50–70 |
| Delicata Squash | Mar 26 | May 21 | May 28 | Aug 20 – Sep 24 | 80–100 |
| Edamame | — | May 21 | — | Aug 6 – Sep 17 | 75–100 |
| Endive | Mar 26 | Apr 30 | May 7 | Jun 25 – Jul 30 | 45–65 |
| Escarole | Mar 26 | Apr 30 | May 7 | Jul 2 – Jul 30 | 50–70 |
| Fava Beans | Mar 26 | Apr 30 | May 7 | Jul 23 – Sep 3 | 75–100 |
| Fennel | Mar 5 | May 21 | May 28 | Jul 30 – Sep 10 | 60–90 |
| Garlic | — | — | — | — | 90–240 |
| Green Beans | — | May 21 | — | Jul 16 – Sep 10 | 50–65 |
| Horseradish | — | — | May 21 | Sep 24 – Oct 15 | 120–180 |
| Hubbard Squash | Mar 26 | May 21 | May 28 | Sep 10 – Oct 15 | 100–120 |
| Kabocha | Mar 26 | May 21 | May 28 | Aug 27 – Sep 24 | 85–100 |
| Kai Lan | Mar 26 | Apr 30 | May 7 | Jun 25 – Jul 23 | 45–60 |
| Kale | Mar 26 | Apr 30 | May 7 | Jul 2 – Aug 27 | 50–70 |
| Kidney Beans | — | May 21 | — | Aug 20 – Sep 24 | 85–110 |
| Kohlrabi | Mar 26 | Apr 30 | May 7 | Jun 25 – Jul 30 | 45–65 |
| Komatsuna | Mar 26 | Apr 30 | May 7 | Jun 11 – Jul 16 | 35–50 |
| Leeks | Mar 26 | Apr 30 | May 7 | Aug 6 – Oct 1 | 90–150 |
| Lentils | Mar 26 | Apr 30 | May 7 | Jul 30 – Sep 10 | 80–110 |
| Lettuce | Mar 26 | Apr 30 | May 7 | Jun 11 – Aug 20 | 30–60 |
| Lima Beans | — | May 21 | — | Jul 23 – Sep 3 | 60–90 |
| Mache | Mar 26 | Apr 30 | May 7 | Jun 18 – Jul 23 | 40–60 |
| Melon | Mar 26 | May 21 | May 28 | Aug 6 – Sep 24 | 70–100 |
| Microgreens | Mar 26 | Apr 30 | May 7 | May 14 – Jun 11 | 7–21 |
| Mitsuba | Mar 26 | Apr 30 | Apr 30 | Jun 25 – Aug 20 | 50–70 |
| Mizuna | Mar 26 | Apr 30 | May 7 | Jun 11 – Jul 9 | 30–45 |
| Mustard Greens | Mar 26 | Apr 30 | May 7 | Jun 11 – Aug 13 | 30–50 |
| Napa Cabbage | Mar 26 | Apr 30 | May 7 | Jul 2 – Aug 6 | 55–75 |
| Onion | Mar 26 | Apr 30 | May 7 | Aug 6 – Sep 24 | 90–120 |
| Pac Choi | Mar 26 | Apr 30 | May 7 | Jun 18 – Jul 16 | 40–55 |
| Parsnip | — | Apr 30 | — | Aug 13 – Sep 24 | 100–130 |
| Patty Pan Squash | Mar 26 | May 21 | May 28 | Jul 16 – Aug 13 | 45–60 |
| Peas | Mar 26 | Apr 30 | May 7 | Jul 2 – Aug 27 | 55–70 |
| Peppers | Feb 19 | May 21 | May 28 | Jul 30 – Oct 8 | 60–90 |
| Pole Beans | Mar 5 | May 21 | May 28 | Jul 23 – Sep 17 | 55–70 |
| Potatoes | Mar 5 | May 21 | May 28 | Aug 6 – Oct 15 | 70–120 |
| Pumpkin | Mar 26 | May 21 | May 28 | Aug 27 – Oct 15 | 85–120 |
| Purslane | Mar 26 | Apr 30 | May 7 | Jun 18 – Jul 23 | 40–60 |
| Radicchio | Mar 26 | Apr 30 | May 7 | Jul 9 – Aug 13 | 60–80 |
| Radish | — | Apr 30 | — | May 28 – Jun 18 | 22–35 |
| Rhubarb | — | — | Jun 4 | — | 365–730 |
| Romanesco | Mar 26 | Apr 30 | May 7 | Jul 23 – Sep 3 | 75–100 |
| Rutabaga | — | Apr 30 | — | Jul 23 – Aug 27 | 80–100 |
| Salsify | — | Apr 30 | — | Aug 13 – Sep 24 | 100–130 |
| Savoy Cabbage | Mar 26 | Apr 30 | May 7 | Jul 16 – Sep 10 | 70–110 |
| Scallions | Mar 26 | Apr 30 | May 7 | Jul 2 – Jul 30 | 50–70 |
| Scarlet Runner Beans | Mar 5 | May 21 | May 28 | Jul 30 – Sep 3 | 60–80 |
| Shallot | Mar 26 | Apr 30 | May 7 | Aug 6 – Sep 24 | 90–120 |
| Shiso | Mar 12 | May 14 | May 28 | Jul 23 – Sep 17 | 50–70 |
| Snap Peas | Mar 5 | May 21 | May 28 | Jul 23 – Sep 17 | 55–70 |
| Snow Peas | Mar 26 | Apr 30 | May 7 | Jul 2 – Aug 27 | 50–65 |
| Soybeans | — | May 21 | — | Aug 13 – Oct 8 | 80–120 |
| Spaghetti Squash | Mar 26 | May 21 | May 28 | Aug 27 – Sep 24 | 85–100 |
| Spinach | Mar 26 | Apr 30 | May 7 | Jun 11 – Aug 13 | 35–50 |
| Squash (Summer) | Mar 26 | May 21 | May 28 | Jul 16 – Sep 17 | 45–65 |
| Squash (Winter) | Mar 26 | May 21 | May 28 | Aug 20 – Oct 15 | 80–120 |
| Sunchoke | — | — | May 21 | Sep 10 – Oct 15 | 110–150 |
| Sunflower | Mar 5 | May 21 | May 28 | Aug 6 – Sep 24 | 70–100 |
| Sweet Corn | — | May 21 | — | Jul 23 – Sep 3 | 60–90 |
| Tatsoi | Mar 26 | Apr 30 | May 7 | Jun 11 – Jul 16 | 35–50 |
| Tomatillo | Mar 5 | May 21 | May 28 | Jul 30 – Oct 8 | 60–85 |
| Tomatoes | Mar 5 | May 21 | May 28 | Jul 30 – Oct 8 | 60–85 |
| Turnip | — | Apr 30 | — | Jun 11 – Jul 16 | 40–60 |
| Watercress | Mar 26 | Apr 30 | May 7 | Jun 18 – Jul 23 | 40–60 |
| Watermelon | Mar 26 | May 21 | May 28 | Aug 6 – Sep 24 | 70–100 |
| Wax Beans | — | May 21 | — | Jul 16 – Sep 10 | 50–65 |
| Zucchini | Mar 26 | May 21 | May 28 | Jul 16 – Sep 10 | 45–60 |
🍓 Fruits to Grow in Thunder Bay
22 fruits that grow well in Zone 4b with planting dates for Thunder Bay.
Show all 22 fruits with planting dates
| Plant | Start Indoors | Direct Sow | Transplant | Harvest | Days to Maturity |
|---|---|---|---|---|---|
| Alpine Strawberries | — | — | Jun 4 | Sep 3 – Oct 29 | 90–180 |
| Aronia | — | — | Jun 4 | — | 730–1095 |
| Blueberries | — | — | Jun 4 | — | 730–1095 |
| Cantaloupe | — | — | Jun 4 | Aug 13 – Sep 17 | 70–90 |
| Cranberries | — | — | Jun 4 | — | 730–1095 |
| Currants | — | — | Jun 4 | — | 730–1095 |
| Elderberries | — | — | Jun 4 | — | 730–1095 |
| Goji Berries | — | — | Jun 4 | — | 730–1095 |
| Gooseberries | — | — | Jun 4 | — | 730–1095 |
| Grapes | — | — | Jun 4 | — | 730–1095 |
| Ground Cherry | — | — | Jun 4 | Aug 13 – Oct 8 | 65–80 |
| Hardy Kiwi | — | — | Jun 4 | — | 1095–1825 |
| Haskaps | — | — | Jun 4 | — | 730–1095 |
| Honeydew | — | — | Jun 4 | Aug 27 – Oct 8 | 80–110 |
| Jostaberry | — | — | Jun 4 | — | 730–1095 |
| Lingonberries | — | — | Jun 4 | — | 730–1095 |
| Medlar | — | — | Jun 4 | — | 1095–1825 |
| Mulberries | — | — | Jun 4 | — | 730–1825 |
| Persimmon | — | — | Jun 4 | — | 1095–2555 |
| Raspberries | — | — | Jun 4 | — | 365–730 |
| Serviceberries | — | — | Jun 4 | — | 730–1095 |
| Strawberries | — | — | Jun 4 | Sep 3 – Oct 29 | 90–365 |
🌿 Herbs to Grow in Thunder Bay
32 herbs that grow well in Zone 4b with planting dates for Thunder Bay.
Show all 32 herbs with planting dates
| Plant | Start Indoors | Direct Sow | Transplant | Harvest | Days to Maturity |
|---|---|---|---|---|---|
| Angelica | Mar 26 | Apr 30 | Apr 30 | — | 365–730 |
| Anise | Mar 26 | Apr 30 | Apr 30 | Jul 30 – Sep 24 | 90–120 |
| Basil | Mar 12 | May 14 | May 28 | Jul 23 – Sep 24 | 50–75 |
| Bee Balm | — | — | May 14 | Aug 13 – Oct 8 | 90–120 |
| Borage | Mar 26 | Apr 30 | Apr 30 | Jun 25 – Aug 13 | 50–60 |
| Caraway | Mar 26 | Apr 30 | Apr 30 | — | 365–450 |
| Catnip | — | — | May 14 | Jul 16 – Sep 17 | 60–80 |
| Chamomile | Mar 26 | Apr 30 | Apr 30 | Jul 2 – Sep 10 | 60–90 |
| Chervil | Mar 26 | Apr 30 | Apr 30 | Jun 11 – Aug 13 | 40–60 |
| Chives | — | — | May 14 | Jul 16 – Sep 24 | 60–90 |
| Cilantro | Mar 26 | Apr 30 | Apr 30 | Jun 11 – Aug 13 | 40–60 |
| Comfrey | — | — | May 14 | Jul 16 – Sep 24 | 60–90 |
| Dill | Mar 26 | Apr 30 | Apr 30 | Jun 11 – Aug 13 | 40–60 |
| Echinacea | — | — | May 14 | Sep 17 – Oct 8 | 120–180 |
| Fennel (herb) | Mar 26 | Apr 30 | Apr 30 | Jul 2 – Sep 10 | 60–90 |
| Garlic Chives | — | — | May 14 | Jul 16 – Sep 24 | 60–90 |
| Horehound | — | — | May 14 | Jul 30 – Sep 24 | 75–90 |
| Hyssop | — | — | May 14 | Jul 23 – Sep 24 | 70–90 |
| Lemon Balm | — | — | May 14 | Jul 16 – Sep 3 | 60–70 |
| Lovage | — | — | May 14 | Jul 23 – Sep 24 | 70–90 |
| Mint | — | — | May 14 | Jul 16 – Sep 24 | 60–90 |
| Oregano | — | — | May 14 | Jul 16 – Sep 24 | 60–90 |
| Parsley | Mar 26 | Apr 30 | Apr 30 | Jul 2 – Sep 3 | 60–80 |
| Rue | — | — | May 14 | Jul 23 – Sep 24 | 70–90 |
| Sage | — | — | May 14 | Jul 30 – Sep 24 | 75–90 |
| Savory | — | — | May 14 | Jul 9 – Sep 3 | 50–70 |
| Sorrel | Mar 26 | Apr 30 | Apr 30 | Jun 11 – Aug 13 | 40–60 |
| Tarragon | — | — | May 14 | Jul 16 – Sep 24 | 60–90 |
| Thai Basil | Mar 12 | May 14 | May 28 | Jul 23 – Sep 24 | 50–75 |
| Thyme | — | — | May 14 | Jul 23 – Sep 24 | 70–90 |
| Valerian | — | — | May 14 | Sep 17 – Oct 8 | 120–180 |
| Yarrow | — | — | May 14 | Aug 13 – Oct 8 | 90–120 |
Monthly Planting Guide for Thunder Bay
Gardening Guides & Resources
Helpful guides from The Ultimate Homestead to improve your garden in Thunder Bay.
Frequently Asked Questions
What planting zone is Thunder Bay, ON?
Thunder Bay is in USDA Hardiness Zone 4b. This zone classification determines which perennial plants survive winter and sets the baseline for frost timing across the county.
When is the last frost in Thunder Bay, ON?
Based on 30 years of NOAA weather station data, the median last spring frost in Thunder Bay falls around May 7. Plan transplants and direct-sow dates relative to this date.
When is the first fall frost in Thunder Bay, ON?
The median first fall frost in Thunder Bay arrives around October 1. Harvest or protect frost-sensitive crops — tomatoes, peppers, basil, squash — before this date.
Is Thunder Bay a good location for home gardening?
Thunder Bay scores 89/100 (Excellent) on our Microclimate Index, which combines frost reliability, drought pressure, soil challenge, elevation risk, and long-term climate trend. This is an above-average location for home gardening with relatively predictable growing conditions.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Thunder Bay gardeners in Zone 4b organize planting dates, track what's growing, and never miss a planting window.
Get Your Free Garden Planner →Free download. Plan your entire garden season in minutes.
