Japanese Stewartia

Stewartia pseudocamellia

Theaceae · broadleaf deciduous tree · introduced

Last updated

Data Coverage 3 of 6 dimensions
Site Data
Threats
Cultivars
Phenology
GDD Thresholds
Puget Sound

Japanese stewartia is a deciduous tree native to Japan, reaching 30-50 feet tall with exfoliating, mottled gray and tan bark. The tree produces white flowers with crinkled petals and orange stamens in midsummer and oblong leaves that turn striking purple-red to orange in fall.

Japanese stewartia thrives in partial shade to full sun with well-drained, acidic, humus-rich soil and consistent moisture. Hardy to zones 5-8, it is slow to medium in growth rate with exceptional ornamental value from flowers, fall foliage, and winter bark. The tree does not tolerate drought stress.

Quick Facts

Height
20–40 ft
Spread
26 ft
Growth Rate
Slow
Light
Part Shade
Soil
Moist
Water
Moderate
Hardiness
Zone Zones 4–5
Bloom Time
June to July
Fall Color
Purple, red, yellow
Origin
Japan

Phenological Calendar

As of April 19, 2026, Puget Sound stations range from 1342.9 to 1500.8 GDD₃₂. Japanese Stewartia typically reaches 'first bloom' at 2878 GDD₃₂, predicted around Jun 15.

Regional Season Tracker

GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 19, 2026
Station GDD₃₂ Current Stage Next To Go
Issaquah / East King 1,501 Pre-season 'First bloom' 1,377
Seattle / UW 1,465 Pre-season 'First bloom' 1,413
Kent / Auburn 1,441 Pre-season 'First bloom' 1,437
Olympia / Tumwater 1,415 Pre-season 'First bloom' 1,463
Bellingham / Whatcom 1,390 Pre-season 'First bloom' 1,488
Tacoma / Puyallup 1,381 Pre-season 'First bloom' 1,498
Sequim / Rain Shadow 1,343 Pre-season 'First bloom' 1,535
Stage GDD32 Typical Window
○ 'First bloom' BBCH '61' NEXT 2878 '' est. Jun 15 (avg)
'Full bloom' BBCH '65' 3498 '' est. Jul 6 (avg)
Regional estimate
Range: 2365–2748 GDD₃₂ (6yr)

GDD = Growing Degree Days (base 32°F, Jan 1 start). Why base 32? Source GDD₅₀ thresholds from Herms 2004 (OSU, Secrest Arboretum, Ohio) and UMD IPMnet (Gill & Klick, mid-Atlantic), converted to GDD₃₂ via Kent bloom-date mapping. Season tracker for Kent / Auburn as of Apr 19, 2026. Predicted dates use 16-day weather forecast through May 5, 2026, then climate normals.