When should I start seeds indoors in Canada?

It depends on your city's last frost date. Count backward from that date using each vegetable's recommended lead time: tomatoes and peppers 6-8 weeks before last frost, broccoli and cabbage 4-6 weeks, cucumbers and squash 3-4 weeks. In Toronto (last frost ~May 10), start tomatoes around mid-March. In Calgary (last frost ~May 22), start around early April.

What vegetables should I start indoors vs direct sow?

Start indoors: tomatoes, peppers, eggplant, broccoli, cabbage, cauliflower, celery, leeks, and onions. Direct sow outdoors: carrots, beans, peas, corn, radishes, beets, and turnips — these do not transplant well or are fast enough to direct sow. Cucumbers and squash can be started indoors 3-4 weeks before last frost or direct sown after frost.

What is hardening off and how do I do it?

Hardening off is the process of gradually acclimatizing indoor seedlings to outdoor conditions before transplanting. Start 1-2 weeks before your transplant date. Day 1-2: set plants outside in a sheltered spot for 1-2 hours. Increase exposure by 1-2 hours each day. By day 7-10, plants can stay out all day. Bring in if frost threatens. Skip hardening off and transplants will suffer transplant shock from sun, wind, and temperature swings.

What should I do if my seedlings are leggy and stretching?

Leggy seedlings are caused by insufficient light. Solutions: move lights closer (5-10 cm above canopy), increase light duration to 16 hours, or move to a brighter location. For tomatoes, you can bury the leggy stem deeper at transplanting — tomatoes grow roots along buried stem sections. For other vegetables, prevent legginess by providing adequate light from germination.

SEED STARTING

When to Start Seeds Indoors Canada — 2026 Planting Calendar

Q: Do I need a grow light to start seeds indoors in Canada?

For most of Canada, yes. A south-facing window gets insufficient light intensity from January through March to produce stocky seedlings. Without supplemental light, seedlings become leggy and weak. A basic 45-100W LED grow light hung 5-10 cm above seedlings for 14-16 hours daily produces much stronger plants than window light alone.

Get a 6–12 week head start on your growing season. City-by-city timing for Toronto, Vancouver, Calgary, Ottawa, Edmonton, Montreal, and more.

Starting seeds indoors is how experienced Canadian gardeners beat our short seasons. In Toronto, your outdoor growing window runs roughly May 10 to October 15 — about 155 days. But with indoor seed starting, you can add 8–12 weeks to that, turning a short season into a genuinely productive one. You'll harvest tomatoes in July rather than September, peppers that actually ripen, and eggplant that would otherwise never mature in our climate.

The single most important variable is your last spring frost date. Every seed starting date counts backward from that number. Get that wrong and the whole calendar is off. Use our Frost Date Calculator to find your exact date before doing anything else.

🇨🇦 Last Frost Dates by Canadian City — 2026

City	Last Spring Frost	Start Tomatoes	Start Peppers
Vancouver, BC	Mar 28	Feb 10	Jan 27
Victoria, BC	Mar 15	Jan 28	Jan 14
Toronto, ON	May 9	Mar 24	Mar 10
Ottawa, ON	May 17	Apr 1	Mar 18
Montreal, QC	May 3	Mar 18	Mar 4
Calgary, AB	May 23	Apr 7	Mar 24
Edmonton, AB	May 20	Apr 4	Mar 21
Winnipeg, MB	May 25	Apr 9	Mar 26
Halifax, NS	May 6	Mar 21	Mar 7
St. John's, NL	Jun 2	Apr 17	Apr 3

Dates based on 50% probability last frost. Get your exact city's frost date →

Complete Seed Starting Calendar — All Vegetables

All timings are counted backward from your last spring frost date. "6 weeks before frost" means count back 42 days from your frost date above to find your start date.

Vegetable	Weeks Before Frost	Germination Temp	Notes
Start Earliest — 10–12 Weeks Before Frost
🧅 Onions	10–12 wks	10–25°C	Slow to germinate; start early
🌿 Leeks	10–12 wks	15–25°C	Long season crop; essential to start early
🥬 Celery	10–12 wks	18–24°C	Tricky; needs warmth & light to germinate
🫐 Artichokes	10–12 wks	18–26°C	Treat as annual in most Canadian zones
Main Season — 6–8 Weeks Before Frost
🍅 Tomatoes	6–8 wks	21–27°C	Most planted indoors crop in Canada
🌶️ Peppers	8–10 wks	24–29°C	Heat mat essential; slow to germinate
🍆 Eggplant	8–10 wks	24–29°C	Long season; must start indoors in Canada
🥦 Broccoli	6–8 wks	15–21°C	Can direct sow too; indoor start gets head start
🥬 Cabbage	6–8 wks	12–21°C	Hardy; can transplant before last frost
🥬 Cauliflower	6–8 wks	15–21°C	Finicky about temperature swings
🥬 Brussels Sprouts	6–8 wks	12–21°C	Long season; essential to start indoors
🥬 Kale & Swiss Chard	6 wks	15–24°C	Can also direct sow after frost
🥬 Head Lettuce	6 wks	15–20°C	For early harvest; leaf lettuce direct sow
Start Late — 3–4 Weeks Before Frost
🥒 Cucumbers	3–4 wks	21–29°C	Don't start too early — they grow fast
🥒 Zucchini & Squash	3–4 wks	21–29°C	Very fast; gets rootbound quickly
🎃 Pumpkins & Melons	3–4 wks	21–27°C	In zones 4–5, start indoors for reliable harvest
🌿 Basil	4–6 wks	21–29°C	Cold-sensitive; don't rush outdoors

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🌱 Seed Starting Calculator ❄️ Find My Frost Date

What NOT to Start Indoors

Just as important as knowing what to start indoors is knowing what to direct sow in the garden. These vegetables do not transplant well and perform better sown directly where they'll grow:

🥕 Carrots

🌱 Parsnips

🌰 Beets

🫛 Peas

🫘 Beans

🌽 Corn

🥬 Spinach

🔴 Radishes

🌿 Dill

🌱 Arugula

How to Start Seeds Indoors — Step by Step

Get the Right Supplies

You need seed-starting mix (not garden soil — it's too dense), seedling trays with cells or small pots, a heat mat ($25–$40, transforms your germination rate), and grow lights. A south-facing window works in a pinch but grow lights produce stronger, less leggy seedlings. Budget $60–$100 for a basic setup that will last years.

Sow at the Right Depth

The general rule is to plant seeds at a depth of 2–3 times their diameter. Tiny seeds like lettuce, basil, and celery get pressed onto the surface and barely covered. Medium seeds like tomatoes and peppers go about 6mm (¼ inch) deep. Large seeds like cucumbers and squash go about 12mm (½ inch) deep. Always check the packet.

Provide Bottom Heat for Germination

This is the step most beginners skip — and the one that makes the biggest difference. Peppers germinate poorly below 24°C and need 29°C for reliable results. Tomatoes benefit from 24°C. A seedling heat mat placed under trays during germination can cut your germination time in half and dramatically improve germination rates. Once seeds sprout, remove from the mat.

Light: 14–16 Hours Daily

This is where most Canadian seed starters fail. In March, even a bright south-facing window only delivers 8–10 hours of light at low angles. Seedlings stretch toward it and become leggy and weak. Grow lights positioned 5–8cm above seedlings, running 14–16 hours daily, produce stocky, strong transplants. Basic LED shop lights work well. A timer makes this effortless.

Water from the Bottom

Pour water into the tray and let seedling cells absorb it from the bottom up. This keeps the soil surface drier, preventing the fungal disease "damping off" — where seedlings suddenly collapse at the soil line. It also encourages roots to grow downward toward the moisture. Let the tray empty within an hour; seedlings sitting in standing water will rot.

Harden Off Before Transplanting

Don't move seedlings straight from a warm house to a cool, breezy garden — the shock will stunt them or kill them. Start 7–10 days before your transplant date. Day 1: set them outside in a sheltered, shaded spot for 1 hour. Increase time and sun exposure each day. Bring them in if temperatures drop below 10°C or if it's windy and cold. By day 7–10 they should handle a full day outdoors. Then transplant on a cloudy day or in the evening.

5 Seed Starting Mistakes Canadian Gardeners Make

Starting Too Early — Seedlings outgrow their cells and become rootbound before it's safe to transplant. Follow the timing chart above closely.

Not Enough Light — The single biggest cause of leggy, weak seedlings. Supplement with grow lights in February and March, no matter how bright your windows look.

Using Garden Soil — Too heavy, doesn't drain properly in cells, may contain pathogens. Always use a dedicated seed-starting mix.

Skipping Hardening Off — Transplant shock can set plants back 2–3 weeks. Always harden off gradually.

Forgetting to Fertilize — Seed-starting mix has very few nutrients. Once seedlings develop their first true leaves, begin fertilizing with a diluted liquid fertilizer every week or two.

Frequently Asked Questions

Do I need a grow light to start seeds indoors in Canada?

For most of Canada, yes — a grow light is strongly recommended. In February and March when you're starting tomatoes and peppers, natural light through windows is too weak and too short. Seedlings grown under a window typically become stretched, pale, and weak. Basic LED shop lights from a hardware store ($30–$50) work well and transform results. If you're in Vancouver or Victoria with a very bright south window, you might manage without, but even there, supplemental light improves seedling quality significantly.

When should I start tomato seeds indoors in Ontario?

For Toronto and most of southern Ontario (last frost around May 9–15), start tomato seeds indoors around March 24 to April 1 — 6 to 7 weeks before your last frost. Ottawa gardeners (last frost May 17–20) should start around April 1–8. Don't be tempted to start earlier; tomatoes that are too large struggle to adjust to outdoor conditions and often get outperformed by properly-timed plants. Use our Seed Starting Calculator for exact dates for your city.

What's the difference between seed-starting mix and potting soil?

Seed-starting mix is specifically designed for germination — it's fine-textured, very light, drains quickly, and is sterile (no weed seeds or pathogens). Potting soil is coarser, heavier, and often contains fertilizer, bark, or large chunks that can impede tiny root development. Regular garden soil is far too dense and may contain diseases. Use seed-starting mix for germination and early seedling growth, then move to potting mix when transplanting into larger containers or outdoors.

When should I start seeds in Calgary or Edmonton?

Calgary's last frost date is around May 23, Edmonton's around May 20. For tomatoes (6–8 weeks before frost), Calgary gardeners should start seeds around April 7–14 and Edmonton around April 4–11. For peppers (8–10 weeks before frost), start around March 24 in Calgary and March 21 in Edmonton. Prairie gardeners often feel the urge to start earlier to compensate for the short season, but leggy overgrown transplants are actually harder to establish. Stick to the timing and use a grow light.

Can I save money by starting seeds indoors instead of buying transplants?

Absolutely — the savings are significant. A packet of 20–30 tomato seeds costs $3–$5. At a garden centre, one tomato transplant costs $5–$8. Starting your own seeds, you can grow 15–20 plants for the price of one purchased transplant. Even after buying seed-starting mix and grow lights (which last for years), the economics are compelling. You also get access to dozens of heirloom and unusual varieties that garden centres never stock.

Plan Your Full Growing Season

Use these tools together to time everything perfectly

🌱 Seed Starting Calculator ❄️ Frost Dates 🌾 Harvest Calculator 🥕 Plant Spacing