Spotting salt damage: A guide to protecting your Peninsula trees

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Aerial view of the san Franisco Bay. Courtesy Getty Images.

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 column.

Much of the Midpeninsula’s soil contains naturally occurring salt, a result of its proximity to the San Francisco Bay, which can quietly damage trees over time. Coastal flooding, storm surge and even the use of recycled irrigation water can introduce additional salt into soils and onto foliage. The result is a lesser-known but serious threat: salt stress.

Salt affects trees by interfering with their ability to absorb water and nutrients. When salt accumulates in the soil, it draws moisture away from roots, making it harder for trees to stay hydrated even when the ground appears moist. Over time, this can mimic drought conditions, weakening trees and leaving them more vulnerable to pests and disease.

Some species are particularly sensitive. Coastal redwoods, for example, are not native to much of the Midpeninsula and are not naturally adapted to hot, dry climates or elevated salt levels. While many have survived locally with potable water, studies across the Bay Area have shown that redwoods can struggle when exposed to recycled water, which typically contains higher salt concentrations. A 2009-2016 study conducted for the city of Palo Alto’s Regional Water Quality Control Plant found measurable impacts on redwoods in areas using recycled irrigation water.

How salt affects trees

Trees exposed to high salt levels may exhibit a range of symptoms, including:

Browning or scorched foliage, especially on the side facing the salt source
Thinning canopy or slowed growth
Discolored bark or early branch dieback

Salt also can damage fine roots and disrupt nutrient uptake, compounding stress over time.

What to watch for this spring

After a winter of tidal flooding, Midpeninsula residents near the bay should keep an eye out for:

Yellowing or browning leaves on evergreens and ornamentals
Premature leaf drop or thinning foliage
Bark discoloration or cracking
Branch tips that appear stunted or dying

These signs may indicate salt stress, particularly in trees planted in low-lying, flood-prone areas or near roads where runoff accumulates.

Late winter and early spring are ideal times to inspect trees, as bare branches make structural issues — including salt damage — easier to spot before new growth begins.

How to help trees recover

Homeowners can take several steps to reduce salt stress and support tree health:

Rinse soil and trunks with fresh water when possible to help flush salt away
Apply mulch around the base of trees to retain moisture and improve soil structure
Choose salt-tolerant species when planting in vulnerable areas
Avoid piling salty debris near tree trunks after flooding

Repeated exposure to salty soils and flooding can challenge even mature trees. But with early detection and proactive care, homeowners can help protect the long-term health of their landscape.

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.