Last Frost Date Saint John NB — When Is It Safe to Plant?
Saint John NB planting guide — Zone 5b (warmest in NB), last frost May 8, first frost October 8, ~153-day season (longest in NB). Full calendar with indoor start and outdoor transplant dates for 20+ vegetables.
Saint John NB's last frost date is May 8 — the earliest in New Brunswick thanks to powerful Bay of Fundy moderation. First fall frost arrives around October 8, giving Saint John approximately 153 frost-free days in Zone 5b — the longest growing season in the province. The Kennebecasis valley communities (Quispamsis, Rothesay, Hampton) sit slightly inland and run 4–14 days later.
For a deeper dive on Saint John NB's frost dates — urban peninsula community-by-community breakdown (Uptown, South End, North End waterfront, West Saint John, East Saint John), Kennebecasis valley microclimate, Bay of Fundy moderation effects, and how Saint John compares to Halifax and Fredericton — see the dedicated Last Frost Date Saint John NB page. Use this guide alongside the seed starting calculator to build your full planting schedule.
Saint John NB at a glance: Last frost May 8 · First frost Oct 8 · Growing season ~153 days (longest in NB) · Hardiness zone 6a (warmest in NB). Cool-season crops start early April; brassicas + onions transplant late April; warm-season crops (tomatoes, peppers, beans, cucumbers) after May 18.
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A printable one-page PDF — seed-starting, transplant, direct-sow and harvest dates for 30+ crops, from your local frost dates.
📅 Saint John NB's Key Frost Dates
Saint John NB Planting Calendar — Full Table
All dates calculated from Saint John NB's average last frost of May 8. Start indoors dates count backward from transplant date. Direct sow dates are when it's safe to plant outdoors.
| Vegetable | Start Indoors | Transplant Out | Direct Sow | Days to Harvest |
|---|---|---|---|---|
| 🍅 Tomatoes | Mar 27–Apr 10 | May 18–25 | — | 55–85 days |
| 🌶 Peppers | Mar 13–27 | May 22–Jun 1 | — | 60–85 days |
| 🥬 Cucumbers | Apr 24–May 1 | May 15–22 | May 15–22 | 50–65 days |
| 🎃 Zucchini / Squash | Apr 24–May 1 | May 15–22 | May 15–22 | 50–60 days |
| 🥦 Broccoli | Apr 3–17 | Apr 29–May 8 | — | 60–80 days |
| 🥭 Cabbage | Mar 27–Apr 10 | Apr 29–May 8 | — | 70–120 days |
| 🧀 Onions (seed) | Feb 27–Mar 13 | Apr 29–May 8 | — | 100–120 days |
| 🧀 Onions (sets) | — | — | Apr 29–May 8 | 65–75 days |
| 🥕 Carrots | — | — | Apr 24–Jun 1 | 70–80 days |
| 🫘 Bush Beans | — | — | May 15–Jun 5 | 50–60 days |
| 🌿 Peas | — | — | Apr 10–25 | 55–70 days |
| 🥕 Lettuce | Apr 10–24 | Apr 29–May 8 | Apr 24–Jun 15 | 45–60 days |
| 🍃 Spinach | — | — | Apr 15–May 15 | 40–50 days |
| 🥦 Kale | — | — | Apr 15–May 8 (+ Aug fall) | 55–75 days |
| 🪒 Radishes | — | — | Apr 10–Jun 10 | 25–35 days |
| 🥔 Potatoes (seed) | — | — | Apr 15–May 5 | 70–110 days |
| 🥦 Garlic (hardneck) | — | — | Oct 1–15 (previous year) | Harvest Jul |
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Saint John NB Month-by-Month Planting Tasks
🌚 February–March
- Start onion seeds indoors (late Feb–early March)
- Start pepper seeds indoors (mid-March)
- Order seed potatoes and tender bedding plants
🌿 April
- Start tomato seeds indoors (early-to-mid month)
- Start broccoli, cabbage, lettuce indoors (mid-month)
- Direct sow peas, radishes, spinach outdoors (mid-month)
- Prepare beds — compost amendment
- Plant seed potatoes (mid-to-late month)
🌺 May
- Transplant brassicas, onions, lettuce (week 1)
- Direct sow carrots, kale, beets (early month)
- Transplant cucumbers, zucchini (after May 15)
- Transplant tomatoes (after May 18)
- Transplant peppers (after May 22)
- Direct sow bush beans (after May 15)
🍅 June–August
- Side-dress with compost (June)
- Mulch heavily for moisture retention
- Harvest peas, lettuce, radishes (June-July)
- Start fall brassicas indoors (July)
- Direct sow fall kale, spinach, lettuce (August)
- Watch for late blight on tomatoes (Bay of Fundy humidity)
🍁 September
- Main harvest: tomatoes, peppers, beans, squash
- Continue fall greens harvest
- Begin curing onions and garlic
🍂 October
- Final harvests — cover frost-sensitive crops
- Plant hardneck garlic (Oct 1–15)
- Mulch garlic beds heavily for overwintering
- Continue harvesting overwintering kale
Best Vegetables for Saint John NB's Climate
Saint John NB's Zone 5b maritime climate gives gardeners more flexibility than the rest of NB. Cool-season strengths: kale (excellent — overwinters with light protection), peas (spring + fall), broccoli (two crops possible), lettuce, spinach, root vegetables. The cool foggy Maritime summers favour these crops over heat-stressed inland varieties.
Warm-season opportunities (longer than rest of NB): full-size beefsteak tomatoes (80–90 days), heirloom peppers, cucumbers, zucchini, even short-season melons in the warmest spots. Bay of Fundy humidity creates significant late blight pressure on tomatoes from August onward — variety selection matters. Choose Defiant PhR, Mountain Magic, Legend, or Iron Lady for reliable blight resistance.
Hardneck garlic planted in mid-October overwinters reliably under snow cover and produces excellent heads — the Bay of Fundy region is reputed for high-quality garlic production. Overwintering kale works in Saint John in a way it doesn't elsewhere in NB — Winterbor planted in August can be harvested fresh through November and again in early spring with row cover protection.
Bay of Fundy Late Frost & Late Blight Protection
Late frost protection: a late frost after May 8 happens roughly 1 year in 5 in Saint John's urban peninsula. Bay of Fundy late frosts are usually -1 to -2°C and arrive with sea fog or cold Atlantic rain. Keep floating row cover (Reemay, Agribon) on hand until May 20. Cloches over individual seedlings on forecast frost nights. Kennebecasis valley gardeners should keep covers ready until May 25–June 1.
Late blight protection (the bigger Saint John challenge): Bay of Fundy humidity creates serious late blight pressure on tomatoes and potatoes from August onward. Mitigation: (1) choose blight-resistant varieties — Defiant PhR, Mountain Magic, Legend, Iron Lady; (2) stake tomatoes for airflow, prune lower leaves; (3) avoid overhead watering; (4) mulch heavily to prevent soil splash on lower leaves; (5) consider a simple plastic rain cover from August onward in the warmest tomato spot.
📍 Atlantic Canada Garden Resources
Plan Your Saint John NB Garden Season
Use the frost calculator for your exact postal code — Kennebecasis valley (Quispamsis, Rothesay, Hampton) runs 4–14 days later than the May 8 Saint John urban average.
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Save to PinterestFrequently Asked Questions
When can I plant my garden in Saint John NB?
Saint John NB's average last frost date is May 8 — the date that determines your outdoor planting schedule. Saint John has the earliest last frost in New Brunswick thanks to Bay of Fundy moderation. Cool-season crops (peas, spinach, radishes, lettuce, kale) can go in 4–6 weeks before that — early April. Brassicas (broccoli, cabbage, cauliflower) and onions can be transplanted out late April. Warm-season crops (tomatoes, peppers, beans, cucumbers, squash) wait until after May 8, typically May 18–25 in the urban peninsula. Kennebecasis valley (Quispamsis, Rothesay, Hampton) gardeners should wait until May 25–June 1.
What is the last frost date in Saint John NB?
Saint John NB's average last spring frost is May 8 (Zone 5b — the warmest hardiness zone in New Brunswick). The Bay of Fundy moderation makes Saint John 7–9 days earlier than Fredericton and Moncton. Urban peninsula and Lancaster: May 5–10. Kennebecasis valley (Quispamsis, Rothesay): May 12–17. Hampton (upper Kennebecasis): May 15–20. Sussex (inland frost pocket): May 17–22. See the dedicated Last Frost Date Saint John NB page for the full 9-community breakdown.
When should I start tomatoes indoors in Saint John NB?
Start tomato seeds indoors 6–8 weeks before Saint John NB's last frost date of May 8 — meaning mid-to-late March. Transplant outdoors May 18–25 once soil reaches 10°C. Saint John's 153-day growing season is the longest in NB and sufficient for most full-season varieties (80–90 day heirlooms, beefsteaks). Bay of Fundy humidity creates late blight pressure from August onward — choose resistant varieties (Defiant, Mountain Magic, Legend) for reliable harvests.
How long is the growing season in Saint John NB?
Saint John NB's growing season runs approximately 153 days — from last frost around May 8 to first fall frost around October 8. This is the longest in New Brunswick and comparable to Toronto's growing season (~197 days falls behind only in absolute terms). Bay of Fundy moderation holds the fall frost off until the water itself starts cooling in mid-October. Kennebecasis valley gets ~140 days; Sussex inland ~130 days.
What vegetables grow best in Saint John NB?
Saint John NB's Zone 5b maritime climate supports both cool-season and full-season warm crops. Cool-season strengths: kale (excellent overwintering), peas (spring + fall), broccoli (two crops), lettuce, spinach, root vegetables. Warm-season opportunities (longer season than most of NB): full-size beefsteak tomatoes, heirloom peppers, cucumbers, zucchini, even short-season melons in the warmest spots. Bay of Fundy humidity creates late blight pressure for tomatoes from August onward — variety selection (Defiant, Mountain Magic, Legend) matters. Hardneck garlic planted in October overwinters reliably and produces excellent heads.
What growing zone is Saint John NB?
Saint John NB's urban peninsula is Zone 5b under the Canadian Plant Hardiness Zone system — the warmest hardiness zone in New Brunswick, comparable to Halifax and Toronto's outer suburbs. Harbourside pockets (South End, North End waterfront) approach Zone 6b. The Kennebecasis valley communities (Quispamsis, Rothesay) drop to Zone 5b. Sussex and inland NB are Zone 5a/5b. Zone 5b allows survival of moderately tender perennials (hardy hydrangeas, climbing roses, some camellias in protected spots) that fail in continental Zone 5 cities.
Can I grow tomatoes in Saint John NB?
Yes — Saint John NB's 153-day growing season is the longest in NB and supports full-season tomato varieties (80–90 day heirlooms, beefsteaks) that struggle elsewhere in the province. Start indoors mid-to-late March, transplant after May 18 in the urban peninsula (May 25–June 1 in Quispamsis/Rothesay, June 1–5 in Hampton). Bay of Fundy humidity creates significant late blight pressure from August onward — choose blight-resistant varieties (Defiant PhR, Mountain Magic, Legend, Iron Lady) for reliable harvests. Plant in the warmest south-facing spot.
Has the last frost passed in Saint John NB?
Saint John NB's average last frost is May 8 (Zone 5b). If today's date is past May 8 and no frost is forecast in the next 10 days, the last frost has likely passed in the urban peninsula. However, in any given year there is roughly a 15–20% chance of a frost after May 8 — Bay of Fundy spring weather can deliver late-season Atlantic cold fronts. Kennebecasis valley gardeners (Quispamsis, Rothesay, Hampton) should wait until May 20–25 for tender crops.
Is it safe to plant tomatoes outside in Saint John NB?
Wait until May 18–25 to transplant tomatoes outdoors in Saint John NB's urban peninsula (May 25–June 1 in Quispamsis/Rothesay, June 1–5 in Hampton/Sussex). Soil should reach 10°C at 5 cm depth. The 153-day season allows full-season varieties, but choose blight-resistant cultivars (Defiant PhR, Mountain Magic, Legend) — Bay of Fundy humidity creates significant late blight pressure from August onward. Stake plants for airflow, mulch to prevent splashing, and remove lower leaves at first flower.
📍 Nearby Cities We Cover
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