Yes, there is pollen in California year-round, driven by the state’s mild winters and extreme geographic diversity. The typical seasonal breaks seen elsewhere are often reduced or eliminated, meaning allergy sufferers manage symptoms for most of the year. This extended season is linked to a climate that allows vegetation to thrive and release pollen across all four seasons.
Why California’s Geography Creates Unique Pollen Zones
The concept of “California pollen” is misleading because the state’s varied geography creates distinct microclimates, each with its own primary allergens and seasonal timing. Coastal regions, including the Bay Area, benefit from milder temperatures and the Pacific Ocean’s moderating influence. This environment fosters the growth of allergenic trees such as cypress, oak, and olive, along with imported species like alder and birch.
Moving inland to the Central Valley and Inland Empire, the geography shifts to hot, dry summers and cooler winters. This environment supports extensive agriculture and favors high levels of grass and weed pollen, including Bermuda grass, rye, and fescue. Reduced air circulation in the valley can lead to higher concentrations of these airborne particles.
Higher-altitude Mountain and Desert regions, such as the Sierra Nevada foothills, experience shorter, more defined growing seasons due to temperature extremes. In these areas, specific high-altitude plants and desert flora, like willow and mesquite, become the dominant allergens for a concentrated period. This diversity means moving even a short distance within the state can expose a person to a completely different set of allergens.
The Extended California Pollen Calendar
California’s mild climate often causes pollen seasons to start earlier and overlap, contributing to the year-round presence of allergens. The annual cycle often begins as early as January or February with the release of tree pollen from species like cedar, juniper, and oak, particularly in Northern and Southern California. This early spring tree season peaks around March and April, leading to high counts of pollen from ash, olive, and sycamore.
As the tree pollen begins to wane, the grass pollen season quickly takes over, typically starting in late spring around April and continuing through the warmer summer months until September. Common culprits during this period include Bermuda grass, bluegrass, and rye grass, which thrive in California’s irrigated landscapes. In agricultural areas, this grass season can be particularly intense and prolonged.
The final major seasonal shift occurs in late summer and fall, when weed pollen becomes the primary concern, generally from August through October or November. Weeds such as ragweed, sagebrush, Russian thistle, and pigweed release their pollen, often peaking in September, especially in the state’s drier, inland areas. While outdoor pollen levels are lowest in December and January, some tree species, like acacia and alder, can still be found pollinating in the mildest parts of the state.
How to Monitor Localized Pollen Counts
Tracking localized pollen counts is the most effective way for allergy sufferers to manage their exposure in California’s complex environment. General forecasts often lack the precision needed, making it important to seek out data specific to your immediate area. The most reliable information comes from stations certified by the National Allergy Bureau (NAB), which is part of the American Academy of Allergy, Asthma, and Immunology (AAAAI).
Certified stations, often operated by local allergists, use specialized equipment like Burkard collectors to measure the number of pollen grains or spores per cubic meter of air. This provides a highly accurate, daily breakdown of specific tree, grass, and weed pollens. Checking these counts through local air quality websites, allergy clinic sites, or weather apps that source NAB data allows for actionable planning. Understanding the daily count enables people to limit outdoor exposure on high-pollen days, especially during peak morning hours, and to adjust medication schedules accordingly.