Planting Guides
When to Plant Onions in Kansas City: Complete Guide + Best Varieties for Zone 6a
Kansas City, Missouri
USDA Zone 6a
Last Frost: Apr 15
Last updated: October 30, 2025
Learn when to plant onions in Kansas City with specific dates for Zone 6a. Compare 6 varieties, get a complete timeline, and discover which onions grow best in Missouri.
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Quick Answer
Plant onions in Kansas City March 15-April 15 for intermediate-day varieties. Plant garlic mid-October for summer harvest.
TL;DR
Plant onions in Kansas City between March 15-April 15 using intermediate-day varieties like Allium cepa 'Candy' or Allium cepa 'Red Wing'. Kansas City's Zone 6a climate with 193-day growing season is perfect for both spring-planted storage onions and fall-planted overwintering types. Plant garlic in mid-October for summer harvest.
Frequently Asked Questions
When exactly should I plant onions in Kansas City for the best bulbs?
Plant onion sets and transplants between March 15 and April 15 in Kansas City. This timing allows 4-6 weeks of cool weather growth before day length triggers bulbing in late June. Allium cepa 'Candy' and Allium cepa 'Red Wing'} are excellent intermediate-day varieties for spring planting. For fall planting, plant overwintering varieties like {Allium cepa 'Walla Walla'} between September 15-October 1.
What onion varieties work best in Kansas City's Zone 6a climate?
Intermediate-day varieties requiring 12-14 hours of daylight work best at Kansas City's 39°N latitude. Allium cepa 'Candy' is the most reliable all-purpose variety, producing large, sweet bulbs consistently. Allium cepa 'Red Wing'} excels for long-term storage, keeping 8-10 months when properly cured. {Allium cepa 'Yellow Sweet Spanish'} produces jumbo bulbs for fresh eating and moderate storage.
Can I plant onions in fall in Kansas City, and will they survive winter?
Yes, Kansas City's Zone 6a climate allows successful fall planting of overwintering onions. Plant varieties like Allium cepa 'Walla Walla'} between September 15-October 1 using transplants only. Mulch heavily with 4-6 inches (10-15 cm) of straw after the first hard frost. Fall-planted onions harvest in early June, 2 months ahead of spring plantings.
How do I know if my Kansas City soil is ready for planting onions?
Test soil workability by squeezing a handful—it should crumble rather than form a ball. Kansas City's clay soil often stays too wet for planting until mid-March. Amend heavy clay with 2-3 inches (5-8 cm) of compost plus coarse sand for drainage. Raised beds work exceptionally well here, improving drainage and allowing earlier planting dates.
Should I plant garlic at the same time as onions in Kansas City?
No, plant garlic in fall and onions in spring for best results. Plant Allium sativum 'Music'} or {Allium sativum 'California Early'} between October 10-25, about 4-6 weeks before the ground freezes hard. Garlic requires cold winter exposure (vernalization) to form proper bulbs and will be ready for harvest in July. Spring-planted garlic rarely forms good bulbs in Kansas City.
What's the biggest mistake Kansas City gardeners make with onions?
Using the wrong day-length variety for our latitude. Kansas City sits at 39°N, requiring intermediate-day onions (12-14 hour daylight trigger). Planting short-day varieties results in premature small bulbs, while long-day varieties may not bulb at all in hot summers. Choose varieties specifically bred for the 35-42°N latitude range like Allium cepa 'Candy'} for guaranteed success.
How do I store onions grown in Kansas City's humid climate?
Kansas City's humidity requires careful curing and storage techniques. After harvest, cure onions in a warm (80-85°F/27-29°C), dry location with good air circulation for 2-3 weeks until outer skins are papery and necks are tight. Store cured onions in a cool (32-40°F/0-4°C), dry location—an unheated garage works well. Allium cepa 'Red Wing'} stores 8-10 months under proper conditions, while sweet varieties should be used within 2-3 months.
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Written By
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William "Bill" Crawford
Bill is a third-generation nurseryman who runs a small family garden center on the outskirts of Kansas City. His grandfather started the business in the 1960s, and Bill took over after working as an ag teacher for a decade. He knows the plants that work in the Kansas City area better than anyone—he's grown most of them himself and watched customers succeed or fail with the rest. Bill specializes in trees and shrubs for the Midwest, perennial borders that handle the region's hot summers and cold winters, and helping customers make sensible choices rather than impulse buys. He writes the way he talks to customers: patient, knowledgeable, and honest about what's worth the money and what isn't.
