April 30 and October 16 look like solid deadlines, but at Pearson airport they’re just the midpoint of a coin flip — half the years run later on one end, earlier on the other. That’s the quiet catch behind Ontario’s roughly 169-day growing season: it’s a provincial average built from one mild, lake-warmed corner near Toronto, and the calendar shifts hard the moment you move away from that shoreline.
The frost window in Ontario
Two dates set the boundaries for nearly every planting decision in this province. Environment and Climate Change Canada’s 1981-2010 Canadian Climate Normals, measured at the Toronto Lester B. Pearson International Airport station, put the average last spring frost at April 30 and the average first fall frost at October 16. Subtract one from the other and you get a frost-free stretch of about 169 days for the Toronto area. For guidance on planning ahead during the coldest, quietest part of the year, see What to Plant in Ontario in January, for what to get into the ground as soon as the soil is workable, see What to Plant in Ontario in March, for what to get into the ground once that spring frost date passes, see What to Plant in Ontario in April, for what to sow in the height of summer to keep the season going, see What to Plant in Ontario in August, and for what to get into the ground once that spring frost date passes, see What to Plant in Ontario in September.
That figure needs a caveat before you plant anything by it. A “normal” frost date is a mean, not a guarantee. Because it’s an average, in roughly half of all years the last frost at Pearson airport falls later than April 30, sometimes by a week or more. Treat the date as the middle of a window, not a green light. The same caution runs in the other direction for fall: in about half the years on record, frost arrives earlier than October 16, cutting the season short from that end instead. For tips on timing your harvest and fall sowing around that date, see What to Plant in Ontario in September, and for planning during the coldest, most dormant month of the year, see What to Plant in Ontario in December. For tips on timing your harvest and fall sowing around that date, see What to Plant in Ontario in October.
Regional differences across the province
Toronto Pearson sits in one of the milder corners of Ontario, close enough to Lake Ontario that the lake moderates temperature swings in both directions. Travel north toward Muskoka, Algonquin, or the upper reaches of Georgian Bay, and the frost-free window shrinks well below 169 days, sometimes by a month or more. Higher elevations and inland pockets away from the Great Lakes lose that buffering effect entirely, so frost settles in earlier in fall and lingers later into spring. Southwestern Ontario, around Windsor and the Niagara Peninsula, often runs a little warmer and longer than the Pearson average because of its own lake exposure and lower latitude.
A provincial planting calendar can only be a starting point given all that. The 169-day figure describes conditions near Toronto specifically, and a gardener two hours north, or simply at a higher elevation, should expect to shift every date in this article later in spring and earlier in fall.
Cool-season crops
Peas, spinach, lettuce, brassicas, and most root vegetables tolerate light frost and germinate best in cool soil, so they go into the ground well before the April 30 average last frost tracked at Toronto Pearson, rather than after it. For a detailed breakdown of what to sow this month, see What to Plant in Ontario in November/ontario/garden/planting-calendar/january/”>What to Plant in Ontario in January, or continue reading below for the full season-by-season guide, via What to Plant in Ontario in February and/ontario/garden/planting-calendar/april/”>What to Plant in Ontario in April. These crops are timed against the frost date itself, not a fixed calendar month, because a mi
Once that last frost date passes and soil temperatures climb further, gardeners can move on to a wider range of warm-season crops. For a detailed month-by-month breakdown, see What to Plant in Ontario in May, which covers what typically goes into the ground once the frost risk has cleared.ld spring can push safe sowing two or three weeks earlier than a cold one would allow.
What goes in first, and why it survives the cold
Peas and spinach are usually the first seeds in the ground, sown as soon as the soil can be worked, often three to four weeks before the last frost date. Both germinate at soil temperatures too cool for warm-season seed, and established seedlings shrug off a light freeze without damage. Lettuce and other leafy greens follow the same logic. Direct-sown lettuce tolerates a frost of a degree or two below freezing, though a hard freeze will still kill young seedlings outright.
Brassica transplants, meaning broccoli, cabbage, kale, and cauliflower started indoors, generally go outside two to three weeks before the last frost date, since they’ve already cleared the tender seedling stage under cover and handle a cold snap outdoors better than a crop started from seed directly in the garden. Root crops such as carrots, beets, radishes, and parsnips are direct-sown around the same window as peas, since germinating seed and young roots aren’t bothered by cool soil the way tomato or squash seed would be.
A few cool-season crops worth targeting for that early window:
- Peas, sown three to four weeks before the last frost
- Spinach and lettuce, sown as soon as soil is workable
- Radishes and carrots, direct-sown alongside peas
- Broccoli, cabbage, and kale transplants, set out two to three weeks before the last frost
- Onion sets and seed potatoes, planted once soil has thawed enough to work
None of these dates assume the ground itself is ready. Cold, waterlogged clay soil left behind by snowmelt in parts of Ontario can delay planting past the calendar window regardless of what the frost date says, so check that a handful of soil crumbles rather than clumps before working it.
Warm-season crops
Tomatoes, peppers, squash, beans, and corn are killed outright by frost, so the April 30 average last frost from Environment and Climate Change Canada is only the starting point for these crops, not the finish line. Soil temperature matters as much as air temperature. Warm-season seed and transplants sit and rot in cold, wet soil even on a frost-free night, so most Ontario gardeners wait one to two weeks after the last frost date before setting out tomatoes and peppers, and longer still for squash, beans, and corn, which want warmer soil to germinate at all.
Tomato transplants show the arithmetic well. Days-to-maturity figures on a seed packet are counted from the transplant date, not from seed, and they shift by a week or two depending on the season’s weather. If a grower sets out transplants in mid-May, about two weeks after the Pearson-area last frost, a 55-day cultivar like Sakura or Edox ripens its first fruit in early July, leaving roughly 100 days of margin before the October 16 average first fall frost. A longer-season type like San Marzano II, at 78 days from transplant, ripens closer to late July and still carries about 77 days of margin, comfortable in most years but worth watching if the season runs cold and late.
Matching tomato cultivars to the season
The table below lines up several catalogue tomato cultivars against a mid-May transplant date and the Pearson-station frost window. All figures are counted from transplant, and the ripening window shifts earlier or later with the actual weather in any given year.
| Cultivar | Days from transplant | Type | Approx. first ripe | Margin before Oct 16 frost |
|---|---|---|---|---|
| Sakura | 55 | Indeterminate | Early July | ~100 days |
| Sun Gold | 57 | Indeterminate | Early July | ~98 days |
| Supersweet 100 | 60 | Indeterminate | Mid July | ~95 days |
| Amalfi | 68 | Determinate | Late July | ~87 days |
| Cherokee Purple | 72 | Indeterminate | Late July | ~83 days |
| Granadero | 75 | Indeterminate | Late July | ~80 days |
| Celebrity Plus | 78 | Determinate | Late July | ~77 days |
For indoor starts, count backward from that mid-May transplant target. Most tomato and pepper seedlings need six to eight weeks indoors before they’re ready to go outside, which puts seed-starting somewhere in late March to early April for a mid-May transplant, adjusted to whatever a given cultivar’s own packet specifies. Squash, beans, and corn are usually direct-sown instead of transplanted, since their roots resent disturbance, and they go into the ground once both air and soil have warmed well past the frost date.
The fall planting window
Working backward from the October 16 average first fall frost, the Pearson-station data gives Ontario gardeners a second planting window that opens in mid to late summer. The logic is the same arithmetic used for spring transplants, just run in reverse. Take a crop’s days to maturity, add one to two weeks to account for the slower growth of shortening fall days, and count back from October 16 to find the latest safe sowing date.
A 30-day radish or a quick bush bean crop still has time for a second planting well into August in the Toronto area, while a 60-day crop needs to go in by mid-summer to mature before that frost date arrives. Even then, remember that October 16 is a mean, not a promise, so a grower in a cooler-than-average year may lose a week or two off the tail end of that math.
Root vegetables and hardy greens are the best candidates for this second window, because several of them improve after a light frost rather than being damaged by one. Kale, Brussels sprouts, and collards convert starches to sugars when touched by cold, producing a noticeably sweeter crop after the first frost or two. Carrots and parsnips left in the ground through a light freeze do the same, which is why many Ontario gardeners leave root crops in place rather than pulling them at the first sign of cold weather.
What to skip in the fall window
Warm-season crops have no place in a fall planting plan here. Tomatoes, peppers, beans, squash, and corn need a long, warm stretch to mature and will not recover from even a light frost, so any warm-season crop still immature by early October is effectively lost once the average frost date arrives. Save the second window for the same cool-season crops used in spring: peas, spinach, lettuce, and the frost-sweetened brassicas and roots above.
Reading a planting calendar properly
A single set of frost dates for an entire province is a convenience, not a forecast for any one garden. The Pearson airport figures used throughout this page describe conditions near Toronto and Lake Ontario specifically. A garden forty minutes north, at higher elevation or further from the lake’s moderating effect, can run a week or two behind those dates in spring and ahead of them in fall, shortening the usable season on both ends.
Urban areas add their own distortion. Pavement, buildings, and reduced wind exposure create a mild microclimate that can push a city garden’s last frost earlier than the surrounding countryside, sometimes by a week or more, which is part of why the same crop can go into a downtown yard before it’s safe in an open field outside town. Lake effect works at a larger scale the same way. The Great Lakes hold heat into fall and delay the first freeze along their shores, while inland areas away from that buffering effect cool off faster once the season turns.
Elevation makes just as much difference in other regions, where mountains and valleys create frost pockets no single station can capture. Wyoming’s growers deal with this at an even larger scale, where elevation swings of thousands of feet shift planting dates by a full month or more across the state, as covered in the Wyoming Planting Calendar.
Building your own record
The most reliable planting calendar is the one a gardener builds by watching their own yard for a season or two: noting the date the last frost actually occurs, watching how quickly soil warms in a particular bed, and tracking which years run early or late compared to the Pearson average. That local record will always beat a single provincial figure, however well-sourced.
Local help
For county-level frost dates, soil testing, and crop recommendations specific to your district, contact Ontario’s Ministry of Agriculture, Food and Rural Affairs through the provincial agriculture and food page. A soil test is worth doing before spring planting, since it tells you what no calendar can: the actual nutrient and pH status of the bed you’re about to plant. Browse our other Ontario guides for crop-specific timing across the province, and see how a very different maritime climate handles the same problem in the Prince Edward Island Planting Calendar.
Common questions
What if my seed packet’s days-to-maturity doesn’t match the numbers on this page?
Use the packet’s own figure as the base and apply the same logic shown above: count from transplant for tomatoes and peppers, add a week or two of slack for cold or cloudy weather, and check the result against the October 16 average fall frost for the Toronto area. Catalogue numbers are consistent from state to state and province to province, but the local frost window is what turns that number into an actual date.
Can I grow a longer-season tomato, like a 90-day heirloom, in Ontario?
It’s riskier than the cultivars listed here, all of which run 55 to 78 days from transplant and leave 77 to 100 days of margin before the average fall frost near Toronto. A 90-day cultivar started at the same mid-May transplant target would clear that frost date by a much narrower margin, and a cold, late season could catch it before the fruit ripens.
Why did my tomatoes barely grow for weeks after I planted them right at the frost date?
Cold soil stalls warm-season roots even when there’s no actual frost damage to the leaves. Tomato and pepper roots grow slowly below a certain soil temperature, so a transplant that goes in the moment the air turns frost-free can sit and sulk for two or three weeks until the soil itself catches up. Waiting the extra week or two after the last frost date, as this page recommends, usually means faster establishment overall, not a slower start.
Do fall-planted crops need more water than spring ones?
Usually yes, at least at the start. A second planting in mid to late summer goes into soil that’s warm and often dry from the season’s heat, so seed for a fall crop of lettuce, spinach, or radishes needs more frequent watering to germinate than the same seed would in cool, damp spring soil. Once seedlings are established, watering needs settle back down closer to normal.
Is it worth buying a soil thermometer instead of just watching the calendar?
For squash, beans, and corn, yes. These crops care more about soil temperature at planting depth than about the calendar date, and a cheap probe thermometer pushed a couple of inches into the bed tells you directly whether the soil has caught up to the air. Air temperature can feel warm on a sunny afternoon while the soil underneath is still too cold for these seeds to germinate reliably.
Related guides
- Manitoba Planting Calendar: When to Sow and Plant, Frost Dates Included
- Quebec Planting Calendar: When to Sow and Plant, Frost Dates Included
- Prince Edward Island Planting Calendar: When to Sow and Plant, Frost Dates Included