When does pollen season start? A timetable for trees, grasses and weeds

Why can't pollen season be counted from one fixed date?

Many people think pollen season starts at the beginning of spring or on some fixed day. In fact, it follows when plants flower. When a plant flowers depends on local temperature, sunlight and rainfall, so the same kind of tree may differ by several weeks between the south and the north. It is more practical to think of pollen season as a series of 'flowering periods' than to remember a single date.

Also, whether pollen can reach your nose depends on the weather. On warm, humid and windy days, pollen levels in the air are often higher, and symptoms are more likely to be triggered. So 'which day it starts' is less accurate than 'which type of pollen is in season now'.

Trees, grasses and weeds: the approximate time periods for three types of pollen

Tree pollen usually comes first. In most regions, early spring to late spring is the main period for tree pollination. Common examples include cypress, poplar, willow and birch. These pollen grains are light and can travel far on the wind, so even if there is no such tree near your home, you may still be affected.

Grass pollen is mostly from late spring to summer. Mowing the lawn or walking in grassland outside the city may make symptoms more obvious. The season for this type of pollen is relatively concentrated, but different grass species flower at different times, so the overall period may last quite long.

Weed pollen is common from late summer to autumn, such as mugwort and ragweed. This type of pollen often matches 'as soon as autumn comes, my nose and eyes itch'. The time periods of the three types of pollen overlap, so some people have more than one uncomfortable stage in a year.

Why is the same season different in different regions?

Our country spans a large north-south distance. For the same type of pollen, the start time in the south is usually earlier than in the north, and the end may also be later. In places with high altitude, the flowering period is pushed back. Coastal and inland areas, and cities and suburbs, have different vegetation, so the dominant pollen types in the air also differ.

So when someone says 'it starts in March', that may not apply to where you live. A more reliable approach is to check locally published pollen monitoring information, and combine it with the timing of your own symptoms in previous years, to gradually work out your own 'pollen calendar'.

How do I check the local pollen forecast?

You can look for pollen level information from the local meteorological department or mainstream weather apps. Some cities give levels separately by tree species or grass species. When looking at the forecast, the key is not to memorise the numbers but to watch the trend: which days are rising, and which days rain will bring a brief drop.

If there is no detailed local pollen forecast, you can use a 'symptom diary' instead: each day, simply note one line about the degree of nose itching, sneezing and eye itching, and compare it with the weather and your time outdoors. After recording for one or two years in a row, you can roughly see your sensitive periods, which fits you better than looking at forecasts alone.

When should I see a doctor?

If you have nose itching, repeated sneezing, clear watery nasal discharge, and itchy, watery eyes at the same time every year, and it lasts for weeks without improving, it is worth getting assessed at a proper medical institution rather than just putting up with it.

See a doctor as soon as possible if any of the following occur: wheezing, chest tightness, difficulty breathing; swelling of the lips or throat, difficulty speaking or swallowing; symptoms suddenly getting worse with general discomfort. These are not ordinary pollen symptoms and need prompt treatment.

Also, if symptoms already affect sleep, work or study, or if relief methods you bought yourself at the pharmacy are not clearly effective, it is also advisable to ask a doctor to assess. Whether further tests are needed and which treatment approach suits you should be decided by a doctor based on your individual situation.

This article is for general information only and is not medical advice. Please follow your doctor's instructions.