Why Pollen Wise Shows Low or Zero Pollen in Winter
As temperatures drop, many of our users wonder why the app seems unusually calm. You might scroll and see a few 0’s listed under each category. Don’t worry: seeing low or zero pollen levels during the late fall and through the winter months is completely normal. Winter is the quietest part of the pollen year, and most plants simply are not releasing pollen this time of year.
If you’re seeing minimal pollen activity in November, December, January, or February, it doesn’t mean the sensor network is offline, and it doesn’t mean something is wrong. This is exactly what we expect to see during winter months. Hopefully, the low levels or absence of pollen in the air means a decrease in allergy symptoms.
Why Pollen Levels Drop During Winter
Pollen is a critical part of the reproductive cycle of most plants. Plants use pollen as a way of transporting their genetic material to another plant of the same species in order to make new seeds. A huge number of plants rely on insects, birds, and animals to transport their pollen, mostly through the use of showy, fragrant flowers with sweet nectar. Plants that use this pollination strategy often produce only a little pollen, since the creatures they are attracting with flowers have a very good chance of finding another flower of the same kind.
However, some plants employ an entirely different strategy: they produce massive quantities of pollen and release it into the wind, where some of it might blow to and land on a compatible flower. These plants will often release pollen at a very specific time to take advantage of weather patterns and flowering timing, to ensure as many seeds are made as possible.
But all that pollen production and seed production costs energy – and plants only get energy from the sun, and only when they have access to enough water. When the weather gets colder and the days grow shorter, many plants either die or go dormant as they await the return of warmer weather. They don’t have the extra energy to devote to making pollen, flowers, and seeds. This makes pollen concentrations much lower in the winter months.
When You Can See Pollen in Winter
Even though winter is low-pollen season, there are a few important exceptions. This is valuable for understanding winter allergies and for users who still see occasional spikes in the app.
Mountain Cedar (Juniperus ashei)
One of the most infamous winter pollens. This species typically pollenates December–February in Central Texas and Southern Oklahoma. This pollen is notorious for causing “cedar fever.”
Early-blooming tree pollen
In regions with milder winters, certain types of trees may begin pollenation as early as late January. These include:
- Alder (Alnus sp.)
- Hazelnut (Corylus sp.)
- Elm (Ulmus sp.)
- Birch (Betula sp.)
- Juniper & Cypress (Family Cupressaceae)
- Poplars, Cottonwoods & Aspens (Populus sp.)
Indoor allergens vs outdoor pollen
Winter is also a time when indoor allergies (dust mites, pet dander, indoor mold) become more noticeable. These are not pollen, but they can cause similar symptoms. Keep an eye out for an upcoming article from us about ways you can keep these allergens at bay in your home and at work.
How the APS400 Measures Pollen in Winter
The APS400 is the sensor that enables our sensor network to provide hourly data. It operates continuously, even when pollen levels are extremely low. The sensor analyzes particles in real time and classifies pollen types using advanced imaging and machine learning.
During the late fall and throughout the winter season, users may notice consistent low values, often near zero. There may be occasional spikes in areas with winter-active species, but generally the low pollen levels in the air will result in stable readings with very little day-to-day change. Keep in mind that weather events like snow, rain, and sleet are likely to reduce the particle counts that are in the air, including dust and mold levels.
When Pollen Season Starts Again
Pollen season begins earlier than many people think. As a general rule, trees start pollenating as early as late January, while grasses typically start in April, and weeds typically start in August.
As temperatures rise and sunlight increases, you’ll see these changes reflected in the app as pollen levels begin climbing again. As spring approaches, the app will begin showing the first signs of tree pollen — the start of a new pollen year.
If you live in an area where cedar fever is common or you experience winter allergies, winter pollen spikes are still possible. Otherwise, enjoy the calm before the storm, because spring pollen season comes quickly.