Western Hazel

Corylus cornuta var. californica

Betulaceae · broadleaf deciduous shrub · native

Last updated March 8, 2026

You recognize California Hazelnut by its rounded habit, heart-shaped deciduous leaves, and distinctive tubular involucre (burr) enclosing edible hazelnuts throughout the understory of coastal California oak and conifer forests, with northern populations in southwestern Oregon.

California Hazelnut reaches 6-12 feet tall in sun to part shade with moderate water needs and excellent drought tolerance once established. It thrives in well-drained, adaptable soils and tolerates poor fertility. Fast-growing with modest lifespan, it suits woodland gardens and native hedgerows. Watch for eastern filbert blight (not yet documented in California populations), powdery mildew, and root weevils. Nuthatches and squirrels harvest nuts readily; wildlife value is substantial.

Plant Profile

Size & Form

Height

5–12 ft

Site Requirements

Light

Full Sun to Part Shade

Hardiness

Zones 5a–8b

Ornamental Interest

Bloom Time

April

Origin

Pacific Northwest native

Powdery MildewHigh

Active Conidial Spread

Wood DecayHigh

Wound Infection Window

Armillaria Root RotModerate

Active Below-ground Growth

Sooty MoldModerate

Heavy Mold Colonization

Diseases: Regionally Documented (19)

Armillaria spp. — primarily A Armillaria Root Rot Pseudomonas syringae pv. syringae Bacterial Blight [VERIFY] Blanks Cryptosporella umbrina Brown Stain Symptom category — not a single disease Canker Catkin Blast Candidatus Phytoplasma pyri Decline/Collapse Syndrome Anisogramma anomala Eastern Filbert Blight Fungal agents (multiple) Kernel Molds Symptom category — not a single disease Leaf Spot Apple mosaic virus (ApMV) Mosaic Mosses and Lichens Multiple obligate biotrophic fungi (Erysiphales: Erysipha... Powdery Mildew Fumago vagans Sooty Mold Daffodil yellow stripe virus (DYVV) Stunt (Dilly) Sunburn Wet Feet Taphrina wiesneri Witches' Broom Multiple Basidiomycete fungi cause wood decay in trees Wood Decay

Phenological Calendar

As of June 3, 2026, Puget Sound stations range from 2435.5 to 2672.8 GDD₃₂. Western Hazel has reached 'leaf emergence' (1161 GDD₃₂) and is approaching 'fall color / leaf senescence', predicted around Jun 16.

Regional Season Tracker

GDD₃₂ accumulation across 7 Puget Sound stations · as of Jun 3, 2026

Station	GDD₃₂	Current Stage	Next	To Go
Issaquah / East King	2,673	'Leaf emergence'	'Fall color / leaf senescence'	335
Kent / Auburn	2,665	'Leaf emergence'	'Fall color / leaf senescence'	343
Seattle / UW	2,610	'Leaf emergence'	'Fall color / leaf senescence'	398
Olympia / Tumwater	2,570	'Leaf emergence'	'Fall color / leaf senescence'	439
Tacoma / Puyallup	2,535	'Leaf emergence'	'Fall color / leaf senescence'	473
Bellingham / Whatcom	2,533	'Leaf emergence'	'Fall color / leaf senescence'	475
Sequim / Rain Shadow	2,436	'Leaf emergence'	'Fall color / leaf senescence'	573

View full calendar (6 stages)

Stage	GDD₃₂	Typical Window	What to Look For
'First bloom' BBCH '61'	557	''	''
'Flower buds visible' BBCH '51'	710	''	''
'Full bloom' BBCH '65'	800	''	''
'Bud break' BBCH '07'	1097	''	''
● 'Leaf emergence' BBCH '11' NOW	1161	''	''
○ 'Fall color / leaf senescence' BBCH '93' NEXT	3008	'' est. Jun 16 (forecast)	''

Regional estimate

Range: 133–1204 GDD₃₂ (11yr) · 175 obs

Source: 'NPN citizen science observations (WA+OR), n=182, median. services.usanpn.org' About GDD₃₂ →

Season tracker for Kent / Auburn as of Jun 3, 2026. Predicted dates use 16-day weather forecast through Jun 19, 2026, then climate normals.

Data Maturity

Baseline Extension data. Expert review underway.