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Showing dates for Purple Top Walla Walla in USDA Zone 7
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Purple Top Walla Walla · Zones 3–9
Growing Details
Zone-by-Zone Planting Calendar
| Zone | Indoor Start | Transplant | Direct Sow | Harvest |
|---|---|---|---|---|
| Zone 3 | February – March | April – May | September – October | July – September |
| Zone 4 | February – March | March – April | September – October | July – October |
| Zone 5 | January – February | March – April | September – October | July – October |
| Zone 6 | January – February | March – April | September – November | June – October |
| Zone 7 | December – January | February – March | September – November | June – October |
| Zone 8 | December – January | February – March | September – December | May – October |
| Zone 9 | November – December | January – February | September – December | May – September |
Complete Growing Guide
Growing Purple Top Walla Walla onions requires patience and proper timing, but the sweet reward is worth the wait. Start by selecting a sunny location with loose, fertile soil that drains well but retains moisture. Work in 2-3 inches of compost or well-aged manure before planting, as these onions are heavy feeders that need rich soil to develop their characteristic large bulbs.
For the best results, start seeds indoors 10-12 weeks before your last frost date. Sow seeds ¼ inch deep in seed starting mix and keep soil consistently moist at 60-70°F. Once seedlings reach pencil thickness (about 6 inches tall), they're ready to transplant. Harden them off for a week before planting outside 4-6 weeks before your last frost.
Space transplants 4-6 inches apart in rows 12 inches apart. Plant at the same depth they were growing in containers, being careful not to bury the developing bulb. If you're in zones 7-9, you can direct sow in fall for larger bulbs the following summer.
Fertilize every 3-4 weeks with a balanced fertilizer until bulbs begin swelling in mid-summer, then stop feeding to encourage proper curing. Keep soil consistently moist but not waterlogged – irregular watering can cause bulb splitting or poor storage quality.
Avoid common mistakes like planting too deep, which stunts bulb development, or continuing to fertilize late in the season, which delays maturity. Stop watering when tops begin yellowing naturally, usually in late summer. The long growing season (up to 300 days in some climates) allows these onions to reach their impressive size, so resist the urge to harvest early.
Harvesting
Purple Top Walla Walla onions are ready when about half the green tops have fallen over naturally and begun yellowing, typically in late August through September. The bulbs should feel firm and solid when gently squeezed at soil level, with papery outer skin beginning to form. Harvest on a dry, sunny day after the soil has had time to dry out from any recent watering or rain.
Loosen soil around bulbs carefully with a fork, then lift the entire plant by grasping the base of the stems, not pulling on the tops which may break. Brush off excess soil gently but don't remove the outer papery layers or cut the roots yet. The necks should feel firm – avoid harvesting any with soft, squishy necks as these won't store well. Timing is crucial with Walla Wallas since they have a shorter storage life than traditional storage onions.
Storage & Preservation
Fresh Purple Top Walla Walla onions require immediate curing after harvest. Spread them in a single layer in a warm, dry, well-ventilated area for 2-3 weeks until necks are completely dry and papery. Unlike storage onions, Walla Wallas have high water content and low sulfur, giving them only 1-3 months storage life even under ideal conditions.
Store cured bulbs in mesh bags or ventilated boxes at 32-35°F with low humidity, checking regularly and using any with soft spots immediately. For longer preservation, slice and freeze them for up to 8 months, or caramelize and freeze in portions. They also pickle beautifully – their mild, sweet flavor makes excellent quick pickles or pickled onion rings. Dehydrating works well too, though you'll lose some of the characteristic sweetness that makes this variety special.
History & Origin
The Purple Top Walla Walla onion originated in Corsica, France, where French soldier Pete Pieri discovered the sweet variety in the late 1800s. Pieri brought seeds back to Walla Walla Valley, Washington around 1900, where the region's unique climate and volcanic soil transformed this already mild onion into something extraordinary. The combination of cold winters, hot dry summers, and low-sulfur soil reduced the onion's pungency while concentrating its sugars.
Local Italian immigrants, particularly the Pieri and other families, began growing these onions commercially in the early 1900s. By the 1980s, Walla Walla onions had gained such a reputation for sweetness that they received protection as a trademarked name – only onions grown in specific counties of Washington and Oregon can legally be called 'Walla Walla' onions. This heirloom variety helped establish the region's agricultural identity and remains one of America's most celebrated specialty onions, often called the 'champagne of onions' for their premium quality and limited growing region.
Advantages
- +Exceptionally sweet flavor with low sulfur content allows fresh eating like an apple
- +Large bulb size often reaches 3-4 inches diameter with proper growing conditions
- +Mild flavor makes them perfect for raw applications and quick cooking methods
- +Heirloom genetics provide true-to-type seeds for saving year after year
- +Premium market value if selling at farmers markets or specialty stores
- +Distinctive purple-tinged skin makes them easily identifiable
- +Caramelizes beautifully due to high natural sugar content
Considerations
- -Very short storage life of only 1-3 months compared to storage onions
- -Long growing season of 125-300 days requires patience and planning
- -Susceptible to downy mildew in humid conditions requiring preventive fungicide
- -High water content makes bulbs prone to soft rot if soil drainage is poor
- -Limited growing zones for best results - struggles in very hot, humid climates
Companion Plants
Plant Together
Carrots
Onions repel carrot fly while carrots help break up soil for onion bulbs
Tomatoes
Onions deter aphids, spider mites, and hornworms from tomato plants
Brassicas (Cabbage, Broccoli)
Onions repel cabbage worms, aphids, and flea beetles
Lettuce
Onions provide natural pest deterrent while lettuce doesn't compete for space
Peppers
Onions help repel aphids and other soft-bodied insects that damage peppers
Strawberries
Onions deter slugs, aphids, and other pests that commonly attack strawberry plants
Roses
Onions help repel aphids, thrips, and may reduce black spot disease
Marigolds
Both plants repel nematodes and various garden pests when grown together
Keep Apart
Beans
Onions can inhibit nitrogen fixation in legumes and stunt their growth
Peas
Allelopathic compounds from onions interfere with pea plant development
Asparagus
Onions can inhibit asparagus growth and reduce spear production
Sage
Both plants compete for similar nutrients and can inhibit each other's growth
Pests & Disease Resistance
Resistance
Moderate resistance to pink root, susceptible to downy mildew and thrips damage
Common Pests
Onion thrips, onion maggot, cutworms
Diseases
Downy mildew, purple blotch, neck rot, pink root