Read it as a range
Alder starts the tree sequence, birch often follows, grass extends into summer, and mugwort overlaps late summer and early autumn. The exact crossover varies by year.
UK seasonal guide
UK pollen calendar
A month-by-month guide to the four pollen types with meaningful UK seasons. It is a broad planning aid, not a prediction that the same type will be high in every city on a given date.
The UK season at a glance
Highlighted months show the configured common window. Spring and summer windows overlap, and local weather can move the start or finish by several weeks.
| Pollen | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Common alderAlnus glutinosa | Typical season | Typical season | Typical season | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Outside the common window |
| Silver birchBetula pendula | Outside the common window | Outside the common window | Typical season | Typical season | Typical season | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Outside the common window |
| Grass familyPoaceae | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Typical season | Typical season | Typical season | Typical season | Outside the common window | Outside the common window | Outside the common window | Outside the common window |
| Common mugwortArtemisia vulgaris | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Outside the common window | Typical season | Typical season | Typical season | Outside the common window | Outside the common window | Outside the common window |
How to use the calendar
Adjust for latitude
The model adds 2 days per degree north of London, capped at 21 days. In Edinburgh, the calculated birch window shifts by 8.9 days.
Check the type you react to
Overall pollen can look low while your trigger is present. Open the relevant species page or city forecast to see the separate rows.
Regional context
Covered cities by region; the calendar itself remains a national guide.
England
Mean city latitude gives a calendar offset of +2 days versus London. Local weather can still move the actual start by two to three weeks.
Scotland
Mean city latitude gives a calendar offset of +10 days versus London. Local weather can still move the actual start by two to three weeks.
Wales
Mean city latitude gives a calendar offset of +0 days versus London. Local weather can still move the actual start by two to three weeks.
Northern Ireland
Mean city latitude gives a calendar offset of +6 days versus London. Local weather can still move the actual start by two to three weeks.
Ireland
Mean city latitude gives a calendar offset of +2 days versus London. Local weather can still move the actual start by two to three weeks.
Questions the calendar cannot answer
Is a highlighted month a pollen forecast?
No. It is a common seasonal window. The city page supplies dated model forecasts.
Why are olive and ragweed not highlighted?
Both are tracked variables, but neither is a significant established UK pollen season. Their species pages explain why the data rows can remain near zero.
Does a later season mean lower pollen?
No. Latitude shifts timing; it does not determine the concentration on a particular day. Weather and local vegetation also matter.
Seasonal sources
Windows: Met Office: pollen seasons, UK government: pollen forecast. Latitude adjustment is a configured planning rule, not an observed start date. Forecast data provenance is on the methodology page.