If you’re one of the roughly 20% of the UK population with hay fever, knowing which pollen is causing your symptoms matters just as much as knowing that pollen counts are high. Different people react to different pollens, and they don’t all arrive at once. The UK pollen season runs from roughly January through to September, with tree, grass and weed pollens taking turns.
This calendar is based on atmospheric data from the SILAM pollen transport model run by the Finnish Meteorological Institute, overlaid with Met Office weather observations and the University of Worcester’s long-term pollen monitoring records. Where we mention 2026-specific trends, those come from our own forecast data at pollencount.org.
January and February: the quiet start
Hazel and alder are among the first trees to release pollen each year, sometimes as early as mid-January in southern England. Most people don’t notice, because counts are low and the symptoms overlap with winter colds. But if you get itchy eyes in February while everyone else is blaming the weather, hazel or alder pollen could be the cause.
In 2026, a long wet spell followed by a sudden warm snap in late February triggered an early burst of alder pollen. Counts in London hit “very high” before March had even started, weeks ahead of the usual schedule.
Yew also pollinates in this window. It produces visible clouds of yellow dust but is actually a fairly weak allergen for most people.
March: things pick up
Ash, elm, willow and poplar join the mix. Birch begins to appear towards the end of the month in the south, though it won’t peak until April. This is when tree pollen allergy starts to become particularly disruptive for the roughly 25% of hay fever sufferers who react to it.
If you live near water, watch for willow and alder, which cluster along rivers and streams. Urban parks tend to have more birch and plane trees, so city dwellers get a different pollen profile from people in the countryside.
March is also when the Met Office typically switches on its official pollen forecast for the season.
April: birch peak
April is dominated by birch. It’s the most allergenic tree pollen in the UK, and a single birch catkin can release millions of grains. Birch pollen also cross-reacts with certain foods such as apples, cherries, hazelnuts, and carrots, so if your mouth itches when you eat these during spring, that may be oral allergy syndrome triggered by the same proteins.
Oak and plane tree pollen overlap with birch in April. Plane trees are common in cities, including London, so if your symptoms are worst on the commute, plane pollen is worth considering.
Pine pollen appears from April onwards. It’s large and visible — the yellow dust on cars — but it causes fewer allergic reactions than smaller, less visible pollens. The grains are too big to penetrate deep into the airways.
May: the handover
Tree pollen fades through May while grass pollen begins to build. This overlap means May can be rough if you’re sensitive to both. Oilseed rape also flowers in May, painting the countryside yellow. Its pollen doesn’t travel far on the wind, but the plant can still irritate the airways.
Grass pollen typically appears from mid-May in southern England and a week or two later further north. The exact timing depends heavily on spring rainfall and soil temperature. A warm, wet April followed by a dry May tends to produce the worst grass pollen seasons, because the grass grows vigorously then releases all at once when the rain stops.
June and early July: peak misery
This is the worst stretch for most hay fever sufferers. Grass pollen, which triggers symptoms in about 95% of people with hay fever, peaks in early June and again in early July. Counts regularly exceed 200 grains per cubic metre on warm, dry, breezy days.
The first peak tends to be the larger one. After it, if you get a spell of heavy rain, there’s a brief window of relief before the second peak. But a sustained dry spell through June can make the two peaks merge into one long, high plateau.
Nettle pollen also ramps up from June and persists through the summer. It’s often overlooked because people associate nettles with stings rather than pollen, but it’s a genuine allergen.
Geography matters here. The eastern half of England tends to see higher grass pollen counts than the west, because it’s drier. Coastal areas and higher ground generally have lower counts. During blocking high-pressure patterns, easterly winds can also carry grass pollen across the North Sea from the continent, adding European pollen to local sources.
Late July and August: the long tail
Grass pollen declines through July but doesn’t disappear entirely until late August or even September. Weed pollens fill the gap. Nettle continues, joined by dock, plantain and mugwort.
Mugwort is worth knowing about because, like birch, it can cross-react with certain foods. If you get oral symptoms in late summer, mugwort could be the underlying sensitisation.
Fungal spores also peak in late summer, especially Alternaria and Cladosporium, which thrive in warm, humid conditions. These aren’t pollen, but they trigger similar symptoms and are picked up by pollen traps. If your “hay fever” is worst in August when pollen counts are supposedly falling, fungal spores may be the real culprit.
September onwards: winding down
By September, most pollen seasons are over. Weed pollen tails off, and the first frosts finish things entirely. A few late-flowering weeds, such as ivy, produce pollen into October, but at low levels.
The main exception is if autumn is unusually warm, which delays the dieback. In recent years, mild autumns have stretched the tail end of the season by two to three weeks compared with the 1990s average.
How 2026 is different
Three things stand out this year:
- Earlier tree pollen. The late-February warm snap after a prolonged wet winter caused an unusually early and intense burst of alder and hazel pollen. Birch season also started about 10 days ahead of the long-term average.
- Wet spring, vigorous grass growth. April 2026 has been warm and wet across much of England and Wales. If May and June turn dry, expect a sharp grass pollen spike as all that growth dries out and releases pollen simultaneously.
- Climate trend. This isn’t unique to 2026, but the pattern is clear in the data: pollen seasons in the UK are starting earlier and lasting longer than they did 30 years ago. Milder winters, earlier springs, and higher CO2 levels are all contributing. The University of Worcester’s records show many spring-flowering trees are now pollinating a month earlier than they did in the early 1990s.
What you can do with this
If your symptoms peak in April, you’re probably reacting to birch. If June is your worst month, it’s almost certainly grass. Figuring out which pollen you react to changes how you prepare:
- Start antihistamines two weeks before your personal season begins, rather than waiting for symptoms to hit.
- Check species-specific forecasts rather than just the generic “high/medium/low” rating.
- Plan outdoor exercise for after rain, or in the late afternoon when pollen counts tend to drop.
- Keep a symptom diary for a season to pin down exactly which weeks are worst for you.
Weather can shift this entire calendar by weeks in either direction, so treat the dates as a rough framework. But even rough timing is better than being caught off guard every year.