What zone is Toronto for planting?

Toronto's urban core is Zone 6b (average annual winter minimum of about -20.6°C to -23.3°C). Its lakeshore neighbourhoods — the Beaches, Leslieville, harbourfront, and the Toronto Islands — are effectively Zone 7a thanks to Lake Ontario's moderating effect, while higher inland districts north of the city (Vaughan, Richmond Hill, north Markham) run cooler at Zone 6a. Toronto's average last spring frost is around May 10 and first fall frost around October 15, giving a frost-free growing season of roughly 155–160 days. For perennial and shrub selection use the zone (6b); for vegetable transplant timing use the frost dates.

What is the warmest hardiness zone in Ontario?

The warmest hardiness zone in Ontario is Zone 7a, found in the extreme southwest — Windsor, Leamington, Kingsville, and the rest of Essex County, plus Pelee Island in Lake Erie (Canada's southernmost point, which some sources rate 7b). This Carolinian corner has the province's earliest last frost (Windsor around April 25), its longest growing season, and enough summer heat to reliably grow crops that struggle elsewhere in Ontario — sweet potatoes, okra, long-season melons, and tender figs in protected sites. It is one of only a handful of inland Zone 7 pockets anywhere in Canada; almost everywhere else that mild is coastal British Columbia.

What zone is Northern Ontario?

Northern Ontario is considerably colder than the populous south. Thunder Bay sits in Zone 3b and Sudbury in Zone 4a (both confirmed in our city dataset). Further north and inland, the zone drops steadily: towns such as Timmins, Kapuskasing, Cochrane, and Chapleau fall into roughly Zone 2b–3a, and the far northern Hudson Bay lowlands (Moosonee, Fort Severn) reach Zone 1 or lower. Because these smaller communities aren't in our city dataset, don't take a single number as gospel — look up your exact town on the Natural Resources Canada Plant Hardiness Zone Map at planthardiness.gc.ca, which maps every location in the country. Northern Ontario gardeners lean on short-season varieties, season-extension (row covers, cold frames, Wall-O-Water), and cold-hardy perennials rated to Zone 3 or below.

How do I find my exact hardiness zone in Ontario?

Three ways, most precise first: (1) Use the official Natural Resources Canada Plant Hardiness Zone Map at planthardiness.gc.ca — enter your address or postal code for a location-specific zone that accounts for local terrain. (2) Use our interactive Zone Finder (growersguide.ca/zone-finder) — click Ontario to see zones and frost dates for cities across the province. (3) Match to the nearest city in the table on this page. Remember that zones can shift by one or two sub-zones within a single municipality: lakeshore and downtown-urban-heat-island sites run warmer, while inland, higher-elevation, and low-lying frost-pocket sites run colder. When a plant tag says 'hardy to Zone 6,' choosing one rated a zone colder than yours is the safe hedge.

What can I grow in my Ontario zone?

Your hardiness zone tells you which perennials, shrubs, and trees will survive a typical Ontario winter; your frost dates tell you when to plant tender vegetables. In Zone 6b (Toronto, Hamilton, London, Niagara) you can grow most perennials sold in Ontario garden centres, plus borderline Zone 7 plants in sheltered spots. In Zone 5b (Ottawa, Kingston, Barrie, Guelph) stick to Zone 5-or-hardier perennials and expect a last frost in mid-May. In Zone 4a Sudbury and Zone 3b Thunder Bay, choose Zone 3–4 perennials (Northern Lights azaleas, hardy roses, most native shrubs) and lean on season-extension for warm-season vegetables. For crop timing, see our Ontario city planting guides linked below and our frost calculator.

Does the hardiness zone change within one Ontario city?

Yes — microclimates routinely move a site one to two sub-zones off the city's headline zone. The three big drivers in Ontario are the Great Lakes (shorelines on Ontario, Erie, and Huron run milder — Toronto's Beaches approach 7a, Hamilton's waterfront is warmer than the mountain), elevation and the Niagara Escarpment (higher ground is colder — Hamilton mountain is 6a while the lower city is 6b), and the urban heat island (dense downtown cores hold winter warmth, while low-lying rural frost pockets and river valleys just outside the city can be a full zone colder). This is why a location-specific NRCan map lookup beats relying on your city's single published number.

ONTARIO PLANT HARDINESS ZONES

Ontario Hardiness Zones — Zone by City & Region

Q: What hardiness zone is Ontario?

Ontario spans a wide range of plant hardiness zones — from roughly Zone 2 in the far north (Hudson Bay lowlands, Moosonee) to Zone 7a in the extreme southwest (Windsor, Essex County, and Pelee Island, which is among the mildest inland sites in Canada). The great majority of Ontarians garden in Zone 5a to Zone 6b: Toronto, Mississauga, Brampton, Hamilton, London, and Niagara are Zone 6b; Ottawa, Kingston, Barrie, and Guelph are Zone 5b; Sudbury is Zone 4a and Thunder Bay is Zone 3b. Zones are assigned by Natural Resources Canada based on winter minimum temperature plus summer heat, rainfall, snow cover, wind, and frost-free days — so a Canadian zone is not identical to the U.S. (USDA) zone of the same number. Check your exact location on the NRCan Plant Hardiness Zone Map at planthardiness.gc.ca.

Q: Are Canadian hardiness zones the same as USDA zones?

No — and this trips up Ontario gardeners who buy plants or read growing advice from U.S. sources. The USDA system is based on winter minimum temperature alone. Natural Resources Canada's system factors in seven variables — winter minimum, summer maximum, frost-free period, rainfall, snow cover, and wind — so a Canadian 'Zone 6' is defined differently from a USDA 'Zone 6,' even though the numbers look the same. NRCan does also publish a separate USDA-method map for cross-border comparison. Practical rule for Ontario: use the Canadian (NRCan) zone from planthardiness.gc.ca for Canadian-sourced plants and seed catalogues, and treat a U.S. plant tag's zone as a rough guide only — when in doubt, pick the hardier (lower-numbered) option.

Ontario hardiness zones run from Zone 3b in Thunder Bay to Zone 7a in Windsor. Find your city's plant zone, last and first frost dates, and growing-season length — then plant with confidence.

Updated July 2026 · Natural Resources Canada Plant Hardiness Zone Map + Environment and Climate Change Canada normals (1991–2020)

Ontario hardiness zones: the province spans roughly Zone 2 in the far north to Zone 7a in the extreme southwest (Windsor, Essex County, Pelee Island). Most Ontarians garden in Zone 5a–6b: Toronto, Mississauga, Hamilton, London, and Niagara are Zone 6b; Ottawa, Kingston, Barrie, and Guelph are Zone 5b; Sudbury is Zone 4a and Thunder Bay is Zone 3b. Zones come from Natural Resources Canada and are not identical to U.S. (USDA) zones of the same number. Find your exact zone at planthardiness.gc.ca or with our interactive Zone Finder.

🍁 Ontario Zones at a Glance

Warmest

Windsor

Zone 7a

Coldest (major city)

Thunder Bay

Zone 3b

Most gardeners

Zone 5a–6b

GTA, east & SW Ontario

Ontario Hardiness Zone by City

Cities below are drawn from our frost-date dataset (Environment and Climate Change Canada normals + Natural Resources Canada zones), sorted from the warmest zone to the coldest. Tap a city with a link for its full month-by-month planting guide.

City	Zone	Last Frost	First Frost	Season
Windsor ›	7a	Apr 25	Oct 20	178 days
Brampton ›	6b	May 12	Oct 12	153 days
Hamilton ›	6b	May 5	Oct 20	168 days
London ›	6b	May 10	Oct 10	153 days
Markham	6b	May 12	Oct 12	153 days
Mississauga ›	6b	May 10	Oct 15	158 days
Niagara Falls	6b	Apr 28	Oct 22	177 days
Toronto ›	6b	May 10	Oct 15	158 days
Barrie ›	5b	May 15	Oct 5	143 days
Guelph ›	5b	May 12	Oct 8	149 days
Kingston	5b	May 10	Oct 10	153 days
Ottawa ›	5b	May 15	Oct 1	139 days
Sudbury ›	4a	May 25	Sep 25	123 days
Thunder Bay	3b	May 28	Sep 20	115 days

Frost dates are historical averages; actual dates vary year to year, so add 1–2 weeks of buffer before transplanting frost-sensitive crops. Zones can shift by a sub-zone or two within a single city (see below).

Ontario's Zones, Warmest to Coldest

Zone 7a — the Carolinian southwest. Windsor, Leamington, Kingsville, Essex County, and Pelee Island (Canada's southernmost point). The province's earliest last frost, longest season, and enough summer heat for sweet potatoes, okra, melons, and sheltered figs.

Zone 6b — the Golden Horseshoe & SW Ontario. Toronto, Mississauga, Brampton, Markham, Hamilton, London, and Niagara Falls. Lake-moderated, densely populated; lakeshore pockets edge into Zone 7a while higher inland ground drops to 6a.

Zone 5a–5b — eastern & central Ontario. Ottawa, Kingston, Barrie, and Guelph. Colder continental winters and a mid-May last frost; choose Zone 5-or-hardier perennials.

Zone 3b–4a — the near north. Sudbury (4a) and Thunder Bay (3b). Short seasons and hard winters; short-season varieties and season-extension are the norm.

Zone 1–3a — the far north. Timmins, Kapuskasing, Cochrane, Chapleau, and the Hudson Bay lowlands (Moosonee). These towns aren't in our dataset — confirm your exact zone on the NRCan map before choosing perennials.

Why Ontario Zones Aren't the Same as U.S. Zones

If you're buying plants or reading growing advice from American sources, don't take a USDA zone at face value. The U.S. system is based on winter minimum temperature alone. Natural Resources Canada's system factors in seven variables — winter minimum, summer maximum, frost-free period, rainfall, snow cover, and wind — so a Canadian "Zone 6" is defined differently from a USDA "Zone 6," even though the number is the same. NRCan publishes a separate USDA-method map for cross-border comparison if you need it.

Practical rule for Ontario: use the Canadian (NRCan) zone from planthardiness.gc.ca for Canadian-sourced plants and seed catalogues, and treat a U.S. plant tag's zone as a rough guide only. When in doubt, pick the hardier (lower-numbered) option.

Source & how to cite: Zone assignments follow the Natural Resources Canada Plant Hardiness Zone Map (planthardiness.gc.ca); frost dates are Environment and Climate Change Canada climate normals (1991–2020). Enter your address on the NRCan map for a location-specific zone that accounts for local terrain.

Ontario City Planting Guides

Your zone tells you what survives the winter; these guides tell you exactly what to sow and transplant, week by week, for your city.

Find your exact zone & what to plant now

Click your province on the interactive map, or jump straight to your city's frost-based planting timeline.

🗺️ Interactive Zone Finder 🌱 What to Plant Now ❄️ Frost Date Calculator

Ontario Hardiness Zones — Zone by City & Region

🍁 Ontario Zones at a Glance

Ontario Hardiness Zone by City

Ontario's Zones, Warmest to Coldest

Why Ontario Zones Aren't the Same as U.S. Zones

Ontario City Planting Guides

Find your exact zone & what to plant now

Get New Guides Before Anyone Else

🌱 GrowersGuide.ca

Outdoor

Indoor

Hydroponics

Rooftop

Site

Top Cities

Popular Houseplants

Free Calculators

Most Popular Articles