The definitive Canadian field guide to cold climate seed starting — which seed to buy, where to buy it, and exactly when to start it, counted from the two dates that actually run your garden.
There is a particular kind of heartbreak known only to northern gardeners. It arrives in late August, when the tomato plant you nursed from February — the one that finally, gloriously, set fruit in the third week of July — is hung with two dozen hard green globes that will never ripen before the first frost turns its leaves to black rags overnight. You did everything right. You started early. You watered, you fed, you staked. And the calendar still beat you.
That heartbreak is almost never a gardening failure. It’s an arithmetic failure — and usually one that was locked in months earlier, at the moment you chose a variety and a start date, long before a single seed touched soil. The plant was never going to make it, because a tomato that needs 85 days to mature cannot fit inside a frost-free window that barely holds 95, especially when several of those weeks are too cold for it to do much growing at all. The math was against you from the packet.
This is the thing almost every seed-starting guide gets wrong for people like us. Search “how to start seeds” and you’ll find the same cheerful advice written, essentially, for somewhere with a seven-month growing season: start six to eight weeks before your last frost, keep them warm, pot them up, plant them out. It isn’t wrong, exactly. It’s just written for a world where the season is long enough to forgive a mistake — where a slow start or a poorly chosen variety costs you a couple of weeks, not the entire harvest. In the Canadian North, the season doesn’t forgive. Here, three decisions made before spring — what seed you buy, where you buy it, and when you start it — quietly decide whether September brings a full pantry or a compost pile of green tomatoes.
This guide is about getting those three decisions right. It’s part seed-buyer’s field guide, part frost-planning manual, part honest gear list from someone who has killed a lot of seedlings under lights. By the end you’ll know how to read a seed packet like a northern grower rather than a Californian one, how to think about where your seed comes from and why it might matter, how to count backward and forward from your two anchor dates so nothing is planted too early or too late, and what equipment actually earns its place on your shelf versus what the catalogues would love to sell you. The reference tables at the end are built to be returned to every January, when the catalogues land and the itch to start returns.
Let’s begin by clearing up the single most common misunderstanding in northern gardening — one that even careful gardeners repeat.
Your hardiness zone is not a planting calendar
Ask a Canadian gardener what zone they’re in and they’ll tell you instantly. Ask them what that number actually means and things get murkier — and the murk causes real, expensive mistakes, because zones get used as a proxy for season length when they were never designed to measure it.
Here’s what a hardiness zone actually is. Canada’s plant hardiness zone map — the national standard, maintained by Natural Resources Canada and Agriculture and Agri-Food Canada — describes long-term perennial plant survival, and it’s calculated from a formula using seven climate variables: the coldest month’s mean daily minimum temperature, the mean frost-free period above 0°C, rainfall from June to November, the warmest month’s mean daily maximum temperature, a winter-harshness index based on January rainfall, mean maximum snow depth, and the maximum wind gust over a 30-year period. It’s a composite portrait of whether a perennial can survive a full year in a place.
This is worth pausing on, because it’s a genuine Canada/US difference that trips people up constantly. The USDA system is a fundamentally different animal — it’s built on a single variable, the average annual extreme minimum temperature, and nothing else. So when an American gardening site says “zone 5,” it is making a narrow statement about winter cold. When the Canadian map says “zone 5,” it is making a broader statement about overall perennial survivability, drawing on snow, wind, rain, and summer heat as well. The two systems are not interchangeable, they don’t line up cleanly, and a Canadian zone number is typically about a zone warmer than the USDA number for the same place. Advice imported from the American gardening internet without translating the zones is one of the quieter ways northern gardeners get led astray.
But here is the part that matters most for this guide, and it’s true of both systems: a hardiness zone is not a planting calendar. It tells you something about what perennials might survive your winter. It does not tell you when to start your tomatoes. Even though the Canadian formula happens to include frost-free period as one of its seven ingredients, the zone number that comes out the other end is a blended survivability index — not a date, not a season length, and not a sowing schedule. You cannot reverse-engineer your planting dates from it.
So what does run the seed-starting calendar? Two dates, and one more number that almost nobody mentions.
The two dates — and the honest truth about what they mean
Your last spring frost (LSF) brackets the start of the tender-plant season: the point after which tomatoes, peppers, squash, and beans can reasonably go outside. Your first fall frost (FFF) closes it. The stretch between them is your frost-free period, and across the Canadian North it varies enormously — from well under a hundred days in the coldest inhabited regions to substantially more in the mildest southern pockets. That range, more than any zone number, is the fact that shapes your garden.
Every seed-starting decision is counted from one of these two dates. Tender crops are counted backward from the last spring frost — “start indoors 6 weeks before last frost” means six weeks before your LSF, not some generic March date imported from a warmer place. Fall and overwintering crops are counted forward toward the first fall frost, so they mature before cold shuts growth down. Get your two dates right and the calendar falls into place. Get them wrong and you’ll start warm-season crops too early (leggy, root-bound seedlings that sulk at transplant) or too late (plants that never finish before the FFF guillotine).
Now the part most guides skip, and it genuinely matters: a frost date is meaningless without two qualifiers.
First, a probability. There is no such thing as the last frost date. What exists is a risk level. Climate data gives frost dates at different probabilities — a date with a 50% chance of frost after it, a 25% chance, a 10% chance, and so on. A “50% date” means that in half of all years, frost will still occur after it. That is not a safe planting date; it’s a coin flip. For tender crops that die outright at a touch of frost, you want a conservative risk level — a date with only a 10% chance of frost after it — and even then, a week of extra patience costs you very little while a killed transplant can cost you the whole crop.
Second, a temperature threshold. “Frost” is not one thing. Canadian agroclimate data distinguishes between light frost (around 0°C), moderate frost (roughly −2°C), and hard frost (around −4°C or colder), and the dates for each are quite different. A hardy brassica shrugs off a light 0°C frost that would kill a basil plant outright. So a frost date table is only useful if you know which threshold it’s built on.
The practical upshot: get your frost dates from a local source that states its station, its reference period, its temperature threshold, and its probability level. A number pulled from a generic website with none of that context is a guess wearing a lab coat. Environment and Climate Change Canada’s climate normals, Agriculture and Agri-Food Canada’s agroclimate data, and provincial agriculture extensions all publish properly qualified frost data. Your nearest long-running weather station is worth more to you than any zone map.
The third number: heat, not just frost
Frost-free days tell you how long your season is. They don’t tell you how warm it is — and for heat-loving crops, warmth is the real currency. Two places can share an identical frost-free period and still behave completely differently for a pepper, because one accumulates far more heat over the season than the other.
Canadian agriculture measures this with heat accumulation metrics — growing degree days (GDD) and, for warm crops especially, Corn Heat Units (CHU), which are used across Canadian agriculture precisely because they capture what frost dates miss: the total warmth available for growth. A cool coastal site and a hot interior valley can have the same number of frost-free days and wildly different capacities to ripen a tomato.
This is why a grower can have “enough” frost-free days on paper and still watch fruit fail to ripen. The season was long enough; it just wasn’t warm enough. So when you’re choosing warm-season varieties, think in terms of both: is my frost-free window long enough, and is my season warm enough? For growers who are short on either, the answer is the same — choose early, fast-maturing varieties, and consider season-extension (row cover, cloches, a greenhouse) to buy both time and heat.
All of which is exactly what Earthkeep’s free Zone Calendar is built to handle: it computes every sowing, transplanting, and succession date as an offset from your region’s actual frost dates, rather than from a generic chart. This article is the “why”; the calendar is the “when.”
Days to maturity: the number that decides your harvest
If your frost window is the space you have to work with, days to maturity (DTM) is the size of the thing you’re trying to fit into it — and matching the two is the whole game in a short season.
Days to maturity is the number, usually printed small on the packet, telling you roughly how long a variety takes from planting to harvest. It sounds simple. It is quietly treacherous, and understanding its traps is what separates growers who eat their tomatoes from those who compost them.
Trap one: the clock doesn’t always start where you think. For direct-sown crops (beans, carrots, radishes, corn), DTM generally counts from the day the seed goes in the ground. But for many transplanted crops — tomatoes and peppers especially — the listed DTM is commonly counted from the date the seedling is transplanted outside, not from the day you sowed it indoors. That’s a widespread convention, not a universal law: definitions genuinely vary between companies and between crops. So the rule is not “assume transplant date” — it’s confirm the seller’s definition for that specific crop and variety. A reputable seed house will tell you; if the catalogue is silent, ask. Getting this wrong by six to eight weeks is entirely possible, and in a short season that’s the difference between a harvest and a lesson.
Trap two: DTM assumes conditions you may not have. Those numbers are typically generated in trial gardens under favourable growing conditions. In cool nights, cold soil, and a heat-poor season, real-world maturity often runs longer than the packet claims. The honest move is to build in a buffer rather than plan to the number exactly.
Trap three: your usable season is shorter than your frost-free season. Your frost-free window might be 100 days, but the first and last weeks of it are cold — soil barely warm, nights near freezing — and heat-loving plants do very little during them. Your effective warm-growing season for a tomato or pepper is meaningfully shorter than the raw frost-free count. This is the heat-units point again, arriving from a different direction.
Put these together and a clear rule emerges: a variety’s days to maturity, plus a realistic buffer, must fit comfortably inside your effective growing season, with room to spare. For a grower with a short frost-free period and limited heat accumulation, that means favouring early varieties — the fast tomato over the long-season one, the early corn over the main-season giant, the quick bush bean over the slow pole variety. That isn’t a compromise or a consolation prize. Choosing varieties bred to sprint is the single most powerful thing a northern gardener can do, and it costs nothing but the discipline to read the packet before falling for the picture.
Genetics and sourcing: a sensible preference, not a magic bullet
Here is a claim you’ll hear often in northern gardening circles, and it deserves a careful, honest treatment rather than an enthusiastic one: buy seed from a company near your latitude, because it’s adapted to your climate.
There’s a real principle underneath it. Local adaptation is a genuine phenomenon. When a seed grower saves seed year after year from the plants that performed best in their conditions, they’re running a slow selection process — and over enough generations, that can shift a population toward traits that suit those conditions: germinating in cooler soil, setting fruit despite chilly nights, resisting the diseases that thrive in a cool damp spring, and reaching maturity fast enough to beat the frost. Seed companies that grow, trial, and select their own seed in a cold climate really are doing some of your variety-screening work for you, and their catalogues really are pre-filtered, to a degree, for conditions like yours.
But the argument gets overstated, and it’s worth being precise about the limits:
- A company’s location is not the same as a variety’s pedigree. Many seed companies — including excellent ones — are partly or largely resellers, sourcing seed grown elsewhere and repackaging it. A company headquartered in Manitoba may be selling you a variety bred in the Netherlands and grown in Oregon. Being near your latitude doesn’t automatically mean the seed was bred, grown, trialled, or selected there.
- “Northern seed germinates in colder soil” is a variety-specific claim, not a regional guarantee. Cold-soil germination is a real, breedable trait, and some varieties genuinely have it. But it doesn’t come automatically bundled with a Canadian return address. Treat it as a property of a variety, evidenced by the catalogue’s own description, not as an average biological benefit of buying local.
- The strongest, best-supported version of the argument is simply this: a seed house that grows and selects its own seed in a climate like yours has more useful knowledge, more relevant trial data, and more honest days-to-maturity numbers for your conditions than one that doesn’t. That’s a genuinely good reason to prefer them — and it doesn’t require any magical claims.
So: prefer regional growers, ask where the seed is actually produced, and read variety descriptions rather than assuming. That’s a sensible preference and a sound purchasing habit. It is not a guarantee, and any guide that tells you it is has crossed from information into marketing.
What does reliably help, regardless of who grew the seed: choosing varieties with short days to maturity, choosing determinate types for crops where you’re racing frost, and — for tomatoes especially — looking for varieties explicitly described and trialled as early or short-season.
Where to buy: an honest guide to Canadian seed companies
A word on how to read this list. Most of the best Canadian seed companies are small, and small companies rarely run affiliate programs — which means a “where to buy” guide bent toward whoever pays a commission would be nearly worthless, and would exclude some of the best growers in the country. So the companies here are listed on merit. Affiliate status, where noted, is stated plainly and separately, and only where it’s been confirmed from the company’s own materials.
Principles for choosing, first:
Distinguish growers from resellers. Some companies grow most of what they sell; others primarily source and repackage. Neither is dishonest, but if regional adaptation matters to you, favour the growers — and don’t hesitate to ask a company directly where their seed is produced. Good ones answer happily.
Look for signals of quality: clearly stated days to maturity (with the counting convention explained), honest germination information, the Safe Seed Pledge, clear open-pollinated/hybrid designations, and — the best sign of all — detailed growing notes that show the company actually grows what it sells.
The larger, full-service houses
West Coast Seeds (westcoastseeds.com), Delta, BC — the most comprehensive and beginner-friendly of the big Canadian houses. Over a thousand varieties spanning vegetables, herbs, flowers, and microgreens; non-GMO; and genuinely excellent educational content, with detailed packets and charts. Their catalogue doubles as a reference library. Affiliate note: West Coast Seeds publicly operates an application-based affiliate program (confirmed on their own affiliate page, verified July 2026).
Vesey’s Seeds (veseys.com), York, PEI — an institution approaching a century old, founded by a Maritime market gardener, with deep experience growing for Canadian conditions. Full line of vegetables, herbs, flowers, bulbs, and season-extension supplies.
OSC Seeds (Ontario Seed Company, oscseeds.com), Kitchener, ON — one of the oldest Canadian-owned packet seed companies, dating to the 1800s, with a large selection of vegetables and a good range of heirlooms.
William Dam Seeds (damseeds.com), Ontario — family-owned for 60-plus years, untreated and non-GMO seed, with a devoted following for unusual varieties and a strong European-influenced selection.
McKenzie Seeds (Brandon, MB) — over a century old and widely stocked in garden centres and big-box stores across the country. T&T Seeds (Manitoba) — seed plus a large selection of hardy Prairie-tested trees, shrubs, and stock.
The regional growers and small seed farms
These are the houses where the “grows its own seed in a hard climate” advantage is most real:
Annapolis Seeds (Nova Scotia, annapolisseeds.com) — begun in 2008 by Owen Bridge as a high-school-aged seed saver, now a Maritime treasure. All their seed is grown in the Maritimes, either on their own farm in Nictaux or by a small network of Nova Scotia and PEI growers — open-pollinated, untreated, and regionally adapted, with a strong focus on maintaining rare varieties. Organic in practice, though not certified. (Note: as of summer 2025 they stopped shipping to US addresses.)
Hawthorn Farm Organic Seeds (Ontario, hawthornfarm.ca) — certified organic, grown largely on their own Ontario farm since 1996, with a genuine commitment to regionally adapted, save-your-own genetics. Signatories to both the Safe Seed Pledge and the Open Source Seed Pledge; strong on rare varieties, natives, and perennials.
Prairie Garden Seeds (Saskatchewan) — family-run, specializing in heirloom and open-pollinated varieties selected in one of Canada’s most demanding growing climates.
The Incredible Seed Company (NS), Hope Seeds (Maritimes), Kitchen Table Seed House (ON), Greta’s Organic Gardens (ON), Terra Edibles (ON, heirloom-focused), and Matchbox Garden & Seed Co. (ON) are all small, values-driven houses worth exploring for open-pollinated and heirloom varieties with regional pedigree.
For a broader map, SeedChange’s Bauta Family Initiative maintains a directory of 150-plus Canadian seed companies organized by province — the best starting point for finding a grower in your own backyard.
Seed-saving: the best long-term source, with real caveats
The most resilient seed strategy of all costs nothing and pays no commission to anyone: save your own. Save seed from your best-performing plants year after year and you become your own small northern selection program, gradually favouring the plants that thrive in your specific soil, latitude, and microclimate. It’s the practice behind nearly every regional seed treasure listed above — each began with someone saving seed from what worked. Organizations like Seeds of Diversity Canada run member seed exchanges and the “Seedy Saturday” events held across the country each late winter, where regionally adapted varieties change hands for the price of showing up.
But seed-saving has rules, and beginners who skip them get disappointing results:
- Save only from open-pollinated (OP) varieties, not F1 hybrids. Seed saved from an F1 hybrid will not come true — the next generation segregates into a grab-bag of the parents’ traits, often losing exactly the qualities you liked. Check the packet: if it says F1 or hybrid, enjoy the plant but buy fresh seed next year.
- Avoid unwanted crosses. Many crops cross-pollinate readily (squash and brassicas are notorious). Maintaining a variety true-to-type requires isolation — distance, timing, or physical barriers — or you’ll gradually blend your carefully chosen variety into something else.
- Rogue ruthlessly, and never save from sick plants. Don’t save seed from off-type, weak, or diseased plants; some diseases are seed-borne and you’ll carry them into next season. Save from your best, healthiest, most true-to-type individuals — that’s the whole selection mechanism.
Do it properly and it’s the most powerful cold-climate tool you have. Do it carelessly and you’ll wonder why your saved tomatoes came out strange.
Starting seeds indoors: the setup that actually works
Now the hands-on part — and the part where, having grown seedlings under lights at commercial density, I’ll tell you plainly which gear earns its keep and which is a way to spend money you could put toward seed. The goal indoors is simple to state and fussy to achieve: produce stocky, dark-green, well-rooted transplants that hit the ground running when the season opens. Leggy, pale, root-bound seedlings — the default result of a warm windowsill — cost you weeks at exactly the point in the year when you have no weeks to spare.
Five things matter, roughly in order of importance:
Light — this one is non-negotiable. The most common seed-starting failure in the North is trying to grow seedlings on a windowsill. In late winter, at our latitudes, there simply isn’t enough light — the days are short and the sun is weak and low — and seedlings respond by stretching desperately toward the glass, producing the pale, floppy growth that never fully recovers. You need supplemental light, positioned close (a few inches above the canopy) and run long (roughly 14–16 hours a day). The good news: you don’t need expensive specialized “grow lights.” Ordinary LED shop lights — the flat 4-foot fixtures sold for garages and workshops — produce plenty of usable light for seedlings at a fraction of the price, and modern LEDs run cool and cheap. Buy this first, and don’t skimp.
Bottom heat — for the heat-lovers, during germination only. This is where a seedling heat mat genuinely earns its place. Peppers, tomatoes, and eggplant germinate slowly and unevenly (or not at all) in the cool soil of a typical late-winter house. A heat mat holding the soil in the warm range transforms pepper germination from a multi-week gamble into a reliable event — and faster, more even germination also helps head off the fungal problems that pick off seedlings. The nuance most beginners miss: you need the heat only until germination. Once seeds have sprouted, take them off the mat; continued bottom heat on emerged seedlings pushes soft, leggy growth. The mat is a germination tool, not a growing tool. Cool-season crops generally don’t need one at all.
A sterile seed-starting mix — not garden soil, not coarse potting soil. Start seeds in a fine, light, sterile seed-starting medium. Garden soil is too heavy, drains poorly in small cells, and carries pathogens and weed seeds. A proper starting mix drains well, holds moisture evenly, and substantially reduces “damping off” — the fungal collapse that fells seedlings at the soil line and is a leading cause of indoor losses. Small cost, outsized effect.
Trays, cells, domes — and the soil-block alternative. You need containers with drainage — cell packs, plug trays, or pots — sitting in a solid tray so you can bottom-water. A clear humidity dome keeps moisture high during germination; remove it once seedlings are up, to discourage fungal problems and encourage sturdiness. For the committed grower, soil blocking — forming self-contained blocks of mix with a hand tool, no pot at all — produces excellent root systems (roots air-prune at the block edge instead of circling) and eliminates plastic. A modest tool investment with a real quality payoff if you start a lot of seed.
Airflow. A small oscillating fan run a few hours a day does two useful things: it discourages the still, humid air fungal diseases love, and the gentle movement prompts seedlings to grow thicker, stronger stems. Cheap, and it noticeably improves transplant toughness.
And an honest word on what you don’t need: elaborate multi-tier hydroponic seedling stations, “smart” grow-light gardens with subscription pods, and premium branded everything are lovely if you enjoy gear, but a shop light, a heat mat, sterile mix, some trays, and a fan will grow better transplants than most of it. Put the savings into more seed and better varieties.
Techniques the North needs that the South skips
Winter sowing: let the cold do the work — carefully
Winter sowing is a beautifully low-tech method well suited to the North, and fittingly it’s credited to gardeners who needed a way to start more seed than their windowsills could hold. The idea: sow seeds in a covered, vented container (the classic is a translucent milk jug with the top cut into a hinged lid and drainage holes punched in the base), then set it outside in winter and largely leave it alone. The jug acts as a miniature greenhouse. Seeds experience natural freeze-thaw cycles and germinate on their own schedule when conditions are right — producing tough, already-hardened-off seedlings that never face the jarring transition from a cozy windowsill to a hostile spring.
But this is a technique that rewards precision, and the enthusiastic version of it oversells its universality. Two cautions the cheerful blog posts tend to skip:
- Frost tolerance alone does not make a crop a good deep-winter-sowing candidate. Prolonged cold exposure can vernalize certain crops — brassicas, onions, and beets among them — triggering them to bolt (run to seed) rather than produce the head, bulb, or root you wanted. A seedling that survives the cold beautifully and then bolts in June has still cost you the crop. Timing and species matter.
- Cold-stratification requirements vary enormously by species, in both duration and moisture conditions. There’s no universal “put it out in January” rule.
So: follow each species’ packet instructions rather than a blanket method. Winter sowing is genuinely excellent for the right seeds — and the right seeds are the ones whose own requirements say so.
Cold stratification: seeds that need winter first
Some seeds — many perennials, natives, and certain herbs and flowers — carry a built-in dormancy that must be broken by a period of cold, moist conditions before they’ll germinate at all. In nature this is a safety mechanism: it stops a seed dropped in autumn from sprouting into the teeth of winter, holding it dormant until it has experienced enough cold to “know” spring is coming. This is cold stratification, and for these seeds, skipping it means they simply won’t sprout no matter how warm and cozy you keep them.
You can stratify deliberately indoors — mixing seed with damp sand or vermiculite and refrigerating it — or let winter do it for free via winter sowing. The two techniques pair naturally: winter sowing is, among other things, the easiest cold-stratification method there is. When a packet says “requires cold stratification” or “sow outdoors in fall,” you’ve found a good candidate. Duration and conditions are species-specific, though — check the packet rather than assuming a standard chill period. (Tender tropicals like tomatoes, peppers, and basil neither need nor tolerate this; they stay indoors under lights.)
Hardening off: the transition that can’t be rushed
A seedling grown indoors has lived a sheltered life — no wind, no direct sun, no temperature swings. Transplanted straight out, it can be shocked, scorched, or wind-whipped to death within a day. Hardening off is the gradual, roughly week-to-ten-day process of acclimating seedlings to outdoor conditions: a couple of hours outside in a sheltered, shaded spot on day one, then progressively longer, sunnier, windier exposure until they can handle a full day and night. In the North this step is doubly important, because spring here is genuinely hostile — intense midday sun, cold nights, and drying winds, often all at once. Rushing it is one of the most common ways northern gardeners lose plants they spent two months raising. (One of winter sowing’s underrated perks: those seedlings are already outside, and harden off automatically.)
Succession planting in a compressed season
In a long season, succession planting — sowing small batches every couple of weeks for a continuous harvest — is a luxury. In a short season it’s a discipline for squeezing more food out of the window you have. The northern version is less about spreading harvest across many months and more about using every available week: a fast crop of radishes or salad greens in and out early, followed by a main crop; or a final planting of quick cool-season greens timed to mature as the first fall frosts arrive (many actually sweeten after a light frost). It leans entirely on your two anchor dates — counting forward from the LSF for early successions, and backward from the FFF for the last ones.
Putting it together: a northern seed-starting rhythm
Here’s how a season flows, built around the two anchor dates. Treat “weeks before/after frost” as the language of your seed packets and your Zone Calendar, not as fixed calendar dates — because your dates depend on your location, your station, and your chosen risk level.
Deep winter. The planning and buying season. Catalogues arrive; make your variety list before you open them (to resist the beautiful-photo impulse buys), prioritizing early-maturing varieties whose days-to-maturity fit your window with room to spare. Order early — popular varieties sell out. Set up any cold-stratification seeds, and start the earliest winter-sown containers for species whose packets call for a long chill.
Late winter (roughly 8–12 weeks before LSF). The slow starters go under lights: onions and leeks first, then peppers and eggplant — slow-germinating heat-lovers that appreciate the long runway and a heat mat.
Mid-spring (roughly 6–8 weeks before LSF). Tomatoes go under lights. Much earlier and they get oversized and leggy before it’s safe to plant out; much later and they won’t have the size to make your short season count.
Approaching the LSF. Hardy transplants can go out under protection as soil warms, after hardening off. Direct-sow the cold-tolerant crops — peas, spinach, lettuce, radishes, carrots, beets — as soon as the soil is workable and has reached their (low) germination thresholds; these don’t wait for the frost-free date. Then, only after your last-frost date has genuinely passed at a risk level you’re comfortable with, and the soil has warmed, the tender transplants and warm-season direct sowings (beans, squash, cucumbers, corn) go out. Bias later here. A plant set out a week “late” catches up fast in warm soil; a plant killed by a late frost may not be replaceable in time.
Summer into fall (counting backward from the FFF). Time final successions of quick cool-season crops to mature before — or pleasantly into — the first fall frosts. Keep row cover and cloches on hand; a single sheet of fabric can extend your effective season at both ends.
The whole rhythm, you’ll notice, is nothing but the two dates with crops arranged around them. In the North, you don’t garden by the calendar on the wall. You garden by your own two frost dates, and everything else is counted from there.
The report: quick-reference tables
Use these as planning ranges, not prescriptions. Germination temperatures, maturity times, and indoor-start windows vary by species, cultivar, indoor conditions, and the transplant size you’re aiming for. Always follow the variety’s packet and your local extension guidance over any general chart — including this one.
Table A — Approximate soil temperature ranges for germination
| Crop group | Approx. minimum | Approx. ideal | Northern notes |
|---|---|---|---|
| Cool-season (spinach, lettuce, peas) | ~2–7°C (36–45°F) | ~10–18°C (50–65°F) | Brave in cold soil; direct-sow early, no heat mat needed |
| Semi-hardy (beets, carrots, cabbage, chard) | ~4–13°C (40–55°F) | ~13–21°C (55–70°F) | Direct-sow roots; brassicas often started as transplants |
| Warm-season (beans, corn, squash) | ~13–16°C (55–60°F) | ~21–30°C (70–85°F) | Wait for warm soil — cold soil means rot, not sprouts |
| Heat-lovers (tomato, pepper, eggplant) | Tomato ~10°C; pepper higher | ~21–29°C (70–85°F), pepper warmer | Heat mat strongly recommended for reliable germination |
Ranges vary by cultivar; confirm on the packet.
Table B — Indoor-start planning ranges (counted from your frost dates)
| Crop | Typical start window | Method | Counted from |
|---|---|---|---|
| Onions, leeks | ~10–12 weeks before LSF | Indoors under lights | Last spring frost |
| Peppers, eggplant | ~8–10 weeks before LSF | Indoors, heat mat | Last spring frost |
| Tomatoes | ~6–8 weeks before LSF | Indoors under lights | Last spring frost |
| Brassicas | Varies widely by type (broccoli, cabbage, kale, Brussels sprouts differ) — follow the packet | Indoors; winter sowing only if the species suits it | Last spring frost |
| Perennials/natives needing chill | Mid-winter; chill duration is species-specific | Winter sowing / stratification | Species requirement |
| Peas, spinach, lettuce, radish | As soon as soil is workable and warm enough | Direct sow | Soil temperature |
| Beans, squash, cucumber, corn | After LSF, in warm soil | Direct sow | After last spring frost |
| Final fall greens | So they mature near the FFF | Direct sow | Backward from first fall frost |
Do not apply a single blanket timing to all brassicas — they differ meaningfully. Confirm per variety.
Table C — Canadian seed companies at a glance
| Company | Location | Known for |
|---|---|---|
| West Coast Seeds | Delta, BC | Huge catalogue, best documentation, beginner-friendly |
| Vesey’s Seeds | York, PEI | Approaching a century of Canadian growing experience; full line |
| OSC Seeds | Kitchener, ON | Est. 1800s; large vegetable range, good heirloom selection |
| William Dam Seeds | Ontario | Untreated, non-GMO, unusual varieties, 60+ years |
| McKenzie Seeds | Brandon, MB | Century-old; widely stocked in stores |
| T&T Seeds | Manitoba | Seed plus hardy Prairie-tested trees, shrubs, stock |
| Prairie Garden Seeds | Saskatchewan | Heirloom/OP, selected in a demanding Prairie climate |
| Hawthorn Farm Organic | Ontario | Certified organic, own-grown, regionally adapted, rare varieties |
| Annapolis Seeds | Nictaux, NS | All seed Maritime-grown (own farm + NS/PEI network); OP, untreated |
Affiliate disclosure: As of July 2026, West Coast Seeds publicly operates an application-based affiliate program, confirmed on their own affiliate page. We have not confirmed affiliate programs with the other companies listed, and their inclusion here is on merit alone. Affiliate arrangements change; treat this as a dated snapshot and confirm directly with any company.
Table D — The northern seed-starting gear list
| Item | Verdict | Notes |
|---|---|---|
| LED shop light (4-ft fixture) | Essential | Buy first. Windowsills fail in northern late-winter light. ~14–16 hrs/day, close to the canopy |
| Seedling heat mat | Essential for heat-lovers | Germination only — take seedlings off once sprouted |
| Sterile seed-starting mix | Essential | Prevents damping-off. Not garden soil, not coarse potting mix |
| Trays + cells + humidity dome | Essential | Bottom-water; remove dome once seedlings emerge |
| Small oscillating fan | Worth it | Discourages fungal disease; builds stronger stems |
| Soil-blocking tool | Nice upgrade | Excellent roots, no plastic; for higher-volume growers |
| Multi-tier hydro seedling “gardens,” subscription pods | Skip | Put the savings into more seed and better varieties |
The decision checklist
- Don’t use your hardiness zone as a planting calendar. It describes perennial survival, not sowing dates.
- Get properly qualified frost dates — from a named station, with a stated reference period, temperature threshold, and probability level. Choose a conservative risk level for tender crops.
- Know your heat, not just your frost. Growing degree days / Corn Heat Units tell you whether your season is warm enough, not just long enough.
- Match days to maturity to your effective season, with a buffer — and confirm how the seller counts DTM for that crop.
- Favour early, fast-maturing varieties ruthlessly; consider determinate types for crops racing the frost.
- Prefer seed houses that grow and select their own seed in a climate like yours — and ask where the seed is actually produced.
- Light is non-negotiable indoors. A shop light beats any windowsill.
- Heat mat for heat-lovers, germination only.
- Sterile starting mix to dodge damping-off.
- Winter-sow only species whose requirements suit it — watch for bolting risk from prolonged cold in brassicas, onions, and beets.
- Harden off over a week-plus. Never rush indoor seedlings into a hostile spring.
- Save seed only from open-pollinated varieties, isolate to prevent crossing, and never save from diseased or off-type plants.
- Bias later for tender crops. A lost plant can’t be re-grown in time.
What this all adds up to
Every generic seed-starting guide is really answering the question “how do I start seeds?” — a fine question with a comfortable answer for most of the continent. But for those of us gardening where the season is short and the winters are long, it’s the wrong question. Ours is sharper and less forgiving: how do I fit a full harvest inside a window that barely holds one?
The answer has three parts, all of them settled before the pleasant business of watering seedlings on a sunny March shelf. Choose the right seed — early-maturing, matched honestly to the days and the heat you actually have. Buy it thoughtfully — from growers who select seed in a climate like yours, asking where it was really produced, and remembering that the best long-term seed source might eventually be your own garden. And start it at the right time — not by a calendar date borrowed from a warmer place, and not by a hardiness zone that was never a planting calendar in the first place, but counted precisely backward and forward from your own two frost dates, qualified by a threshold and a probability you’ve chosen with your eyes open.
Do that, and the late-August heartbreak of hard green tomatoes becomes a memory rather than a ritual. The season is still short. The winters are still long. But a grower who has matched the right seed to the right source to the right moment isn’t fighting the calendar anymore — they’re working with the honest window they have, and filling it. That’s the whole art of gardening in the North: not pretending the season is longer than it is, but knowing it exactly, and packing it full.
This guide is part of Earthkeep’s seed-starting and frost-planning series for cold-climate Canadian growers. Frost dates, variety availability, soil-temperature thresholds, agroclimate data, and company details all change. Confirm current frost dates for your own location — with a stated station, threshold, and probability — and check with seed companies directly on sourcing and programs before planning your season. Start with your free Zone Calendar for the dates that anchor everything above.
Earthkeep sometimes earns a commission when you buy through links on this page, at no extra cost to you. We only recommend seeds and gear we’d put in our own cold frames. Recommendations here are editorial and never paid placements.
Read next
- When to start tomatoes indoors in Canada — why the standard advice starts you two weeks early, and how to find your own date.
- Grow lights for seed starting: what you actually need — the three numbers that matter, and the two that are marketing.