onion

Allium cepa

Amaryllidaceae · bulb · introduced

Last updated April 19, 2026

On Puget Sound clay soils, amend heavily with compost or grow in raised beds. Long-day types preferred at this latitude. Walla Walla sweet onion is the iconic PNW variety.

— Claude / Chris Welch

Plant Profile

Size & Form

Height

1-2 ft

Spread

0.5-1 ft

Growth Rate

Moderate

Lifespan

Short-lived

Site Requirements

Light

Full Sun

Soil Drainage

Well Drained

Soil pH

6.0-7.0

Water

Moderate

Drought Tolerance

Low

Hardiness

Zones 3–10

Ornamental Interest

Bloom Time

June-July (second year if bolting)

Origin

Central Asia (likely Iran/Afghanistan region)

Downy MildewModerate

Late Spring - Summer Transition

Diseases: Regionally Documented (3)

Botrytis Blight (Gray Mold) Multiple obligate oomycetes (Peronosporaceae); species ar... Downy Mildew Stromatinia cepivora (syn. Sclerotium cepivorum) White Rot

Pests: Regionally Documented (2)

Delia antiqua Onion Maggot Thysanoptera Thrips

Cultivars (2)

'Walla Walla'

Long-day sweet onion. Very mild flavor; large bulbs. Poor storage life (1-2 months). The iconic PNW onion.

Transplant in early spring for summer harvest

'Copra'

Long-day storage onion. Firm, pungent, excellent keeper (6+ months).

Data Maturity

Structured Multiple sources. Expert review underway.