12 min read · Allergies
Canada's three pollen seasons
- Tree pollen (spring): birch, maple, oak, poplar, alder and cedar. Starts as early as February on the BC coast and around April in most of the country.
- Grass pollen (late spring to summer): usually late May to July.
- Weed pollen (late summer to fall): ragweed is the big one in Ontario, Quebec and the Maritimes, typically mid-August until the first hard frost.
Mould spores also rise in damp weather and in the fall when leaves decay.
Region by region
| Region | What to expect |
|---|---|
| BC coast | Earliest tree season (alder, cedar) and long, mild seasons; damp climate means more mould |
| Prairies (AB, SK, MB) | Shorter seasons; poplar and birch in spring, grass and weeds in summer; dust from dry fields and wind |
| Ontario & Quebec | Strong tree season, then grass, then heavy ragweed in late summer; city smog adds irritation |
| Atlantic Canada | Seasons start a little later; moist air favours mould |
| The North | Short, intense summer pollen season |
Check daily pollen forecasts from a weather service in your area, as timing shifts each year.
Keeping pollen out of your home
- Upgrade your filter: pollen is relatively large, so MERV 8 catches most of it, but MERV 11 or MERV 13 also catches the finer fragments and mould spores that trigger symptoms.
- Run the furnace fan on high-pollen days so indoor air keeps cycling through the filter.
- Keep windows closed on high-pollen and windy days; use AC instead.
- Change your filter at the start of each pollen season.
- Shower and change clothes after time outdoors; keep shoes at the door.
- Run a HEPA purifier in the bedroom – you spend a third of your life there.
- Control humidity at 30–50% to limit mould and dust mites.
Filters reduce allergens in the air but don't replace medical care. Talk to your doctor or an allergist about testing and treatment.