Sherry outlines climate‑resilient garden trees and practical care for Pacific Northwest gardeners

Sherry, the webinar presenter, told listeners that selecting trees with climate resilience is increasingly important as the Pacific Northwest warms and faces longer droughts and more extreme weather. She opened with three guiding questions—how trees cope with climate change, which species suit local gardens, and what constitutes good tree care—and said registrants would receive resource links after the session.

She summarized research on leaf turgor loss point, citing Ulrik Schulman’s measurements at Kew Gardens showing large differences among species in how long their cells remain turgid under drought. "If you take a look at the graph, the trees in the bottom have the highest leaf turgor loss point and therefore more drought tolerant," she said, and added that the study found a strong correlation between higher wood density and greater drought tolerance because denser xylem resists cavitation during dry periods.

Sherry recommended considering drought tolerance and wood density when choosing street and urban trees and noted that parks and gardens that receive higher levels of care can include a mix of drought‑tolerant and faster‑growing species. She highlighted a range of species as examples: silver linden, certain red maple cultivars (which vary in drought tolerance), ginkgo (often planted as male trees to avoid messy fruit), and several native choices OSU researchers recommend as replacements for ash affected by emerald ash borer—cascara, western crabapple, Oregon white oak, and Willamette Valley ponderosa pine.

On pests, Sherry warned that Oregon white oak faces a threat from the Mediterranean oak borer. She advised homeowners to look for branch dieback and to "note the location, take a picture if you can, and report to the Oregon invasive species hotline," which she said triggers expert assessment.

Describing the effects of the June 2021 heat dome, Sherry said damage was widespread—from arboretums to city streets—and that trees in the hottest areas showed reduced growth or even shrinkage a year later; she summarized that roughly "50% of the trees within cities show dried out leaves" in the hardest‑hit areas. To adapt, she suggested considering species that originate from warm climates: manzanitas (for lean, sunny sites), cork oak and strawberry tree (evergreen options), olives (noting winter hardiness is being tested in Oregon trials), chitalpa (a hybrid suited to drier sites but not humid summers), silverleaf oak and other warm‑origin species.

Sherry emphasized the importance of siting and sizing trees before planting: consult mature height and root‑zone estimates, follow USDA guidance on clearances (for example, suggested minimum distances from pavement and buildings shown on her slides), and avoid crowding trees into undersized spaces where roots will later cause infrastructure problems. For planting technique she advised digging a hole at least twice the root‑ball width, correcting circling roots, setting the root flare at or above soil level, and using a 4‑inch layer of fresh wood‑chip mulch kept away from the trunk.

On watering, Sherry recommended slow, deep sessions—delivered by drip, soaker hose, or infrequent bucket fills—through an establishment period. While the exact length varies with tree size, she offered a practical rule: water for roughly three years after planting for many trees, with daily watering during the first two weeks, every 2–3 days up to three months, then weekly. For established trees she advised checking soil moisture 6–8 inches deep and applying supplemental deep water when the root zone (about 12–18 inches) is dry.

During a live Q&A, a participant asked when a tree is considered established; Sherry said it varies by size—months for small specimens, several years for large transplants—and clarified that transplanting volunteer small trees is reasonable in fall when natural rainfall helps establishment. She also agreed that pine bark beetle attacks are often tied to drought‑stressed trees and reiterated that keeping trees properly watered reduces pest risk.

Sherry closed by noting she had shared resource links (OSU publications, extension watering guides, and landscape plant databases) and invited attendees to email for further questions. "I invite you to get out, be among trees, and be inspired by them," she said.