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| Welcome to our tree column, “Ask your local arborist.” Each month, arborist George Reno from the Davey Tree Expert Company in Menlo Park discusses a tree-related topic from general care and planting tips to how trees can impact your property. If you have a tree-related question or an idea for a topic to discuss, email lifestyle@embarcaderopublishing.com or post in the comments section at the end of this colum |
In spring, trees leaf out and bloom, bringing fresh greenery across the landscape. For many residents, it also signals the start of allergy season across the Bay Area.
Tree pollen levels typically rise from March through early June, making this one of the most challenging times of the year for allergy sufferers. The yellow dust coating cars often gets the blame, but it’s not always the main culprit.
The visible, powdery pollen that shows up on sidewalks and windshields is often from pine trees. While it may look dramatic, pine pollen is less likely to trigger severe allergies. Instead, it’s the finer, windborne pollen from hardwood trees, like oaks, that tends to cause the most irritation.
Around the greater Palo Alto area, you may notice small bumps on the leaves of coast live oaks this time of year. They’re caused by tiny insects called gall wasps and don’t harm the trees. Still, they’re a visible reminder that spring is a busy season in the local urban forest.
Bay Area trees that tend to trigger allergies
In the Bay Area, some of the biggest contributors to spring allergies include:
- Walnut: Typically produce peak pollen in April, with shedding continuing through June.
- Oak, especially coast live oak: Oaks have a long pollen season from March to mid-April.
- Juniper, cedar and cypress: Tend to release high-allergen pollen from January to May.
- Olive: A significant source of late-spring allergy pollen.
- Birch: Releases pollen in late March and early April.
These trees release lightweight pollen that travels easily on the wind, making it hard to avoid.
For those in more urban areas, Pollen often feels worse. Part of the reason has to do with how urban trees are chosen. Historically, cities have favored planting male trees because they don’t produce fruit or seeds, which makes for less cleanup. But male trees are also the ones that produce pollen. When there are a lot of male trees and not many female trees to help absorb it, more pollen ends up staying in the air.
While you can’t eliminate pollen entirely, there are ways to reduce its impact, especially when planning your landscape. Knowing your season can help: tree pollen typically peaks in early spring before giving way to grass pollen in summer. Planting strategically also makes a difference. Consider adding lower-pollen or female trees to help balance your landscape. Choosing allergy-friendly options can further reduce exposure; trees such as magnolia, crape myrtle, ginkgo and Japanese maple tend to produce less allergenic pollen and perform well in Bay Area conditions. Finally, diversifying your planting with a mix of species can help reduce the concentration of any one type of pollen.
George Reno is a local arborist at The Davey Tree Expert Company in Menlo Park, which serves communities on the Peninsula, including Menlo Park, Atherton, Palo Alto and Redwood City. Reno can be reached at 866-923-5658.
