March 18 is the number Vancouver-area tomato growers build their whole season around — the average date of the last spring frost, tallied from thirty years of weather records at the airport. It sounds precise. It isn’t a promise. Half the years on record saw frost linger past that mark, sometimes into April, which is exactly why transplants set out the moment the calendar clears March feel safe and often aren’t. The real planting window starts a little later than the math suggests.
What this comes down to in British Columbia
Tomato transplant timing in British Columbia comes down to one number: Environment and Climate Change Canada’s 1981-2010 climate normals put the average last spring frost at March 18, recorded at Vancouver International Airport. The average first fall frost at the same station lands around November 10. Between those two dates sits a growing window wide enough to ripen almost any tomato in the catalogue, but the March figure is where most gardeners misjudge the risk.
That March 18 date is a mean, not a cutoff. Environment and Climate Change Canada calculates it from three decades of data, which means in roughly half of those years the last frost actually fell after March 18, sometimes well after. Treat it as the middle of a risk curve, not a green light. A tomato transplant set outside on March 19 carries no more protection than one set out in February. This is exactly why growers who count back from the frost date still wait until early April, giving the risk a few extra weeks to clear before soft, frost-tender transplants go into the ground.
The span between the two frost dates, roughly eight months from mid-March to mid-November, is generous by Canadian standards, and it is a big part of why growing tomatoes in British Columbia works well along the coast without a greenhouse. But that window belongs to one station near sea level. The Fraser Valley, Vancouver Island, the Okanagan, the Kootenays and anywhere at elevation run on a different clock, and a garden two hours from Vancouver by car may need transplants set several weeks later for the same reason a colder microclimate pushes its own frost dates further into the season from both ends. For a full list of cultivars matched against this window once the transplant date is settled, see Tomato Varieties That Ripen in Time in British Columbia.
Working it out for your own garden
The method matters more than any single date, because the date changes as soon as the address does. Start from Environment and Climate Change Canada’s mean last frost of March 18, recorded at Vancouver International Airport, and treat it as the midpoint of a risk band rather than a hard line. Add a few weeks of buffer to cover the half of years when frost lingers past the mean, and the result is early April as a practical transplant date for the Lower Mainland. From there, the arithmetic is simple: take the cultivar’s days-to-maturity figure printed on the seed packet and count forward from the transplant date to estimate the first ripe fruit.
A short-season cultivar, worked through
Sakura is rated at 55 days from transplant. Set it out in early April and the first ripe fruit should appear about 55 days later, in late May. Count forward from there to Environment and Climate Change Canada’s mean first fall frost of November 10, also recorded at the Vancouver station, and the harvest window runs roughly 168 days past that first ripe fruit before frost is expected to end the season. That is the kind of margin that lets a coastal garden here carry a second flush of fruit well into fall.
A longer-season cultivar, worked through
Granadero needs 75 days from transplant. Set out at the same early-April date, its first ripe fruit lands closer to mid-June, and the margin before the mean November 10 frost narrows to about 148 days. That is still a wide cushion on the coast. The line only gets tight if the transplant date slips, if a cold spring pushes planting into late April or later, or if the garden sits somewhere colder than the Vancouver reference station, where the whole season starts later and ends sooner than these figures describe.
| Cultivar | Days from transplant | Transplant date | First ripe fruit | Margin before mean fall frost |
|---|---|---|---|---|
| Sakura | 55 | Early April | Late May | 168 days |
| Amalfi | 68 | Early April | Early June | 155 days |
| Granadero | 75 | Early April | Mid June | 148 days |
Run the same three columns for any cultivar in the catalogue and the pattern holds: on this coastal frost window, days-to-maturity barely matters, because even the slowest option finishes with nearly five months to spare before the mean fall frost.
The mistakes this state punishes
The frost normals above come from a single coastal station, and the most common mistake in this province is applying them to a garden that isn’t coastal. Vancouver Island, the Lower Mainland, the Interior and the North do not share a frost calendar, and a gardener in a colder pocket who plants by the Vancouver mean risks losing transplants to a frost the coast never saw that year.
- Setting transplants out right at the mean last frost date, rather than after it, because the mean means frost arrives later in half of all years.
- Trusting an early warm spell in March as proof the cold is over, when a clear, calm night that follows a warm stretch is exactly when radiative frost forms.
- Planting into soil that is still cold from winter even after the air has warmed, which stalls tomato roots regardless of the calendar date.
- Assuming a variety’s days-to-maturity figure is fixed, when catalogue numbers are measured under favorable conditions and run a week or two longer in a cool, cloudy spring.
- Ignoring elevation and local frost pockets: a garden in a valley bottom or at higher elevation can run weeks behind the reference station even within the same region.
The fix for all five is the same. Treat the Vancouver-area frost dates as a starting estimate, watch your own soil and sky rather than the calendar, and build in a buffer on both ends of the season rather than planting or expecting harvest right at the mean.
The same caution applies at the other end of the season. Because the mean first fall frost of November 10 at Vancouver International Airport is also an average, some years bring frost weeks earlier than that. A grower who leaves the last tomatoes on the vine expecting the average date, rather than watching the forecast as autumn closes in, can lose a late harvest to a frost that arrived on the early side of that half of years.
Checking this against your county
Every figure on this page comes from one weather station at Vancouver International Airport, and British Columbia is too large and too varied for one station to speak for it. Check your own frost record with a local weather station or a nearby gardener before locking in a transplant date, especially if you garden in the Interior, the North, or at elevation, where both frost dates can shift by weeks in either direction.
The British Columbia Ministry of Agriculture and Food publishes further growing guidance for the province, and your regional office is the right place to ask about conditions specific to your county before committing a season’s worth of seedlings to a single date.
Common questions
Can I plant tomatoes outside in March in BC?
Not safely, in most of the province. March 18 is only the average last frost recorded at Vancouver International Airport, which means frost arrives after that date in roughly half of all years. Wait until soil and air have both warmed, which for most coastal gardens means early April, and later still away from the coast.
What if I’ve already got transplants outside and a late frost is forecast?
Cover them. A bedsheet, row cover or overturned bucket over each plant overnight can hold off a light frost, and it costs nothing to do even if the forecast turns out mild. Pull the cover off in the morning once temperatures climb, since trapped moisture and heat under plastic can do its own damage on a sunny day.
Does the frost date change much between Vancouver Island and the Interior?
Yes, and this page cannot tell you by how much, because the only figures here come from the Vancouver International Airport station. The Interior and northern parts of the province run colder and typically see a later last frost and an earlier first fall frost than the coast. Ask your regional extension office or check a local weather station for your area’s own normals before setting a date.
Is November 10 the last day I can harvest tomatoes outside?
No, it is an average, not a deadline. Some years the first fall frost at Vancouver International Airport arrives well before November 10, and some years well after. Watch the actual forecast as autumn approaches rather than counting on the mean date, and pick remaining fruit ahead of any night frost is expected, ripe or not.