Walla Walla Sweet Onion
Allium cepa
Juicy, sweet, regional favorite. In the Northwest, which has normal low winter temperatures above -10°F (-23°C), seed is sown in late August, and a crop of very large, flattened, ultra-mild onions is harvested early the next summer. SPRING PLANTING: Walla Walla may be spring planted using seeds or plants in colder regions where winter survival is hit or miss. It is not as big or sweet as the wintered-over crop, but still milder and juicier than others from spring planting. Nice as a "green top" onion. Not for storage. Adaptation: 35-55° latitude. Also offered organic, and as plants.
Harvest
125-140d
Days to harvest
Sun
Full sun
Zones
5–10
USDA hardiness
Height
12-18 inches
Planting Timeline
Showing dates for Walla Walla Sweet Onion in USDA Zone 7
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Walla Walla Sweet Onion · Zones 5–10
Growing Details
Zone-by-Zone Planting Calendar
| Zone | Indoor Start | Transplant | Direct Sow | Harvest |
|---|---|---|---|---|
| Zone 3 | — | — | May – June | September – October |
| Zone 4 | — | — | April – June | September – October |
| Zone 5 | — | — | April – May | August – November |
| Zone 6 | — | — | April – May | August – November |
| Zone 7 | — | — | March – May | July – November |
| Zone 8 | — | — | March – April | July – December |
| Zone 9 | — | — | February – March | June – December |
| Zone 10 | — | — | January – March | May – December |
Complete Growing Guide
Light: Full sun (6 or more hours of direct sunlight a day). Soil: High Organic Matter, Loam (Silt), Sand. Soil pH: Alkaline (>8.0), Neutral (6.0-8.0). Drainage: Good Drainage, Moist. Height: 1 ft. 0 in. - 1 ft. 6 in.. Spread: 0 ft. 6 in. - 1 ft. 0 in.. Spacing: Less than 12 inches, 12 inches-3 feet. Maintenance: Medium. Regions: Coastal, Mountains, Piedmont.
Harvesting
Flowers wither and convert to bulblets
Type: Capsule.
Harvest time: Summer
Bloom time: Summer
Storage & Preservation
Walla Walla sweet onions are not long-term storage varieties due to their high water content and low sulfur levels. Store fresh onions in a cool, dry place with good air circulation — never in plastic bags. At room temperature, they'll keep 2-3 weeks; refrigerated, up to 2 months.
For preservation, freezing works exceptionally well for Walla Wallas. Chop and freeze in portions for cooking — they'll last 6-8 months. Their natural sweetness makes them perfect for caramelizing and freezing in recipe-sized portions.
Dehydrating is another excellent option due to their low sulfur content. Slice thin and dehydrate at 125°F until crisp. Pickled Walla Walla onions showcase their mildness beautifully — use a basic vinegar brine with minimal spices to let their sweetness shine through. Store pickled onions in the refrigerator for up to 3 months.
History & Origin
Walla Walla sweet onions trace their roots to the late 1800s when French soldier Peter Pieri brought onion seeds from the island of Corsica to the Walla Walla Valley in southeastern Washington. The unique combination of the valley's volcanic soil, cold winters, and warm summers created ideal conditions that transformed these Mediterranean onions into something extraordinary.
Local Italian and French immigrants recognized the potential and began selecting the sweetest, mildest bulbs for seed saving. By the 1900s, these onions had developed their distinctive characteristics — exceptional sweetness, low sulfur content, and the ability to be eaten raw like fruit.
The variety gained national recognition in the 1980s when promotional efforts highlighted their unique qualities. Today, Walla Walla Sweet Onions are protected by both trademark and geographic designation, with only onions grown in specific counties in Washington and Oregon legally carrying the name. This heirloom represents over a century of careful selection and adaptation to the Pacific Northwest's unique growing conditions.
Advantages
- +Disease resistance: Black Walnut, Deer, Rabbits
Considerations
- -Toxic: Low severity
Companion Plants
Plant Together
Carrots
Onions repel carrot flies while carrots help break up soil for onion bulb development
Tomatoes
Onions deter tomato hornworms and aphids, while tomatoes don't compete for nutrients
Cabbage
Onions repel cabbage worms, cabbage loopers, and other brassica pests
Lettuce
Shallow-rooted lettuce doesn't compete with onion bulbs and benefits from onion's pest-repelling properties
Peppers
Onions deter aphids and other soft-bodied insects that commonly attack pepper plants
Strawberries
Onions repel slugs, aphids, and other strawberry pests while not competing for space
Roses
Onions repel aphids, black spot fungus, and other rose pests when planted nearby
Broccoli
Onions deter cabbage moths and flea beetles that commonly damage brassicas
Keep Apart
Beans
Onions can inhibit bean growth and nitrogen fixation, reducing bean yields
Peas
Onions stunt pea growth and interfere with their nitrogen-fixing capabilities
Asparagus
Onions can inhibit asparagus spear development and overall plant vigor
Nutrition Facts
Per 100g serving. % Daily Value based on 2,000 calorie diet. Source: USDA FoodData Central (FDC #170000)
Pests & Disease Resistance
Resistance
Moderate resistance to pink root and fusarium basal rot
Common Pests
Onion thrips, onion maggots, cutworms
Diseases
Pink root, fusarium basal rot, downy mildew, purple blotch