Planting Timeline
Showing dates for Stuttgart in USDA Zone 7
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Stuttgart · Zones 3–9
Growing Details
Zone-by-Zone Planting Calendar
| Zone | Indoor Start | Transplant | Direct Sow | Harvest |
|---|---|---|---|---|
| Zone 3 | February – March | May – June | April – May | August – September |
| Zone 4 | February – March | May – June | April – May | August – September |
| Zone 5 | February – March | April – May | March – April | July – September |
| Zone 6 | January – February | April – May | March – April | July – September |
| Zone 7 | January – February | March – April | February – March | June – August |
| Zone 8 | December – January | March – April | February – March | June – August |
| Zone 9 | November – December | February – March | January – February | May – July |
Complete Growing Guide
Stuttgart onions thrive in cool climates and perform best when you give them a long growing season. Start preparing your site in fall by working in 2-3 inches of well-aged compost or manure, as these onions demand rich, loose soil that drains quickly.
For the longest bulbs and best storage quality, start Stuttgart from seed indoors 10-12 weeks before your last frost date. Sow seeds ¼ inch deep in seed trays, keeping soil consistently moist at 65-70°F. Once seedlings reach pencil thickness (usually 6-8 weeks), trim tops to 4 inches to encourage strong root development. In zones 3-5, this indoor start is essential for proper bulb formation.
Transplant seedlings when soil temperature reaches 50°F and they can withstand light frost. Space plants 4-6 inches apart in rows 12 inches apart—closer spacing produces smaller bulbs that store longer. Plant so the root crown sits just at soil level; burying too deep restricts bulb development.
Fertilize with a balanced 10-10-10 fertilizer at planting, then switch to lower nitrogen (5-10-10) once bulbs begin forming in early summer. High nitrogen late in the season creates thick necks that reduce storage life. Side-dress with compost monthly until midsummer.
Stuttgart's flat-topped shape makes it prone to sitting in water, so ensure excellent drainage. Hill soil slightly around plants if your area receives heavy spring rains. Stop watering when tops begin yellowing naturally—usually 2-3 weeks before harvest.
Avoid the common mistake of harvesting too early. Stuttgart needs those full 110-120 days to develop proper storage characteristics. Also resist the urge to bend tops over; let them fall naturally as the bulb matures.
Harvesting
Stuttgart onions are ready when 50-75% of the tops have fallen over naturally and turned brown, typically in late summer. The remaining green tops should feel loose and papery at the neck. Test readiness by gently lifting a bulb—mature Stuttgart onions will have developed their characteristic flat top and tight, golden outer skin.
Harvest on a dry morning after several rainless days. Carefully lift bulbs with a fork, working from the side to avoid piercing. Brush off excess soil but don't wash—moisture trapped under the papery skin promotes rot. The bulbs should feel firm and heavy, with necks that are completely dry and tight. If any show thick, fleshy necks, use these fresh rather than storing them.
After lifting, lay Stuttgart onions on screens or newspaper in a well-ventilated area out of direct sunlight. This initial curing period of 7-10 days allows the outer skins to fully tighten and protects the bulbs during long-term storage.
Storage & Preservation
After curing, Stuttgart onions store exceptionally well in cool (32-40°F), dry conditions with good air circulation. Properly cured bulbs keep 6-8 months in a root cellar, unheated garage, or basement. Store in mesh bags, braided strings, or shallow boxes—never in plastic bags which trap moisture.
For shorter storage, keep Stuttgart onions at room temperature in a pantry for 2-3 months. Avoid storing near potatoes, which release gases that cause onions to sprout.
Stuttgart's firm texture makes it excellent for freezing when chopped—no blanching needed, though they'll lose crispness. These onions also dehydrate beautifully into flakes or powder. For longer preservation, Stuttgart's sharp flavor works well in pickled relishes and chutneys, maintaining good texture through the canning process.
History & Origin
Stuttgart onions originated in the fertile valleys surrounding Stuttgart, Germany, where they've been cultivated since the early 1800s. German farmers developed this variety specifically for its exceptional storage qualities—essential for surviving harsh European winters when fresh vegetables were scarce.
The variety gained popularity among German immigrants to America's Midwest in the mid-1800s, who brought seeds in their carefully guarded collections. Stuttgart became particularly valued in Wisconsin, Minnesota, and the Dakotas, where its cold tolerance and storage life made it indispensable for frontier families.
This heirloom represents classic German breeding priorities: reliability over flashiness, storage over immediate consumption, and adaptation to short, cool growing seasons. Unlike many modern hybrids bred for uniform appearance, Stuttgart was selected purely for performance—explaining its somewhat variable shape but consistently excellent keeping quality. Today, it remains largely unchanged from those original German strains, making it a true culinary and agricultural heritage variety.
Advantages
- +Exceptional storage life of 6-8 months when properly cured
- +Excellent cold tolerance allows early spring planting in zones 3-5
- +Flat-topped shape provides more usable flesh per bulb than round varieties
- +Good resistance to pink root disease that devastates other onion varieties
- +Reliable bulb formation even in cool, short-season climates
- +Sharp flavor when fresh mellows beautifully when cooked or caramelized
- +Dense, firm texture holds up well in long-cooking dishes like stews
Considerations
- -Requires long 110-120 day growing season, challenging in very short-season areas
- -Flat shape can collect water and rot if drainage is poor
- -Must be started from seed indoors in most climates—sets rarely available
- -Variable bulb shape and size compared to modern hybrid varieties
- -Susceptible to thrips damage which can reduce storage quality
Companion Plants
Plant Together
Carrots
Alliums repel carrot flies while carrots help break up soil for onion bulb development
Tomatoes
Onions deter tomato hornworms and aphids while improving tomato flavor
Cabbage
Onions repel cabbage worms, cabbage loopers, and flea beetles
Lettuce
Onions provide pest protection without competing for nutrients, complementary root depths
Peppers
Alliums deter aphids and spider mites that commonly attack pepper plants
Broccoli
Onions repel cabbage family pests including cabbage root fly and aphids
Roses
Onions help prevent black spot and repel aphids, Japanese beetles, and other rose pests
Strawberries
Onions deter slugs, aphids, and other soft-bodied pests that damage strawberry plants
Keep Apart
Beans
Onions can inhibit bean growth and nitrogen fixation by rhizobia bacteria
Peas
Alliums can stunt pea growth and interfere with their nitrogen-fixing capability
Asparagus
Onions may inhibit asparagus growth and can compete for similar soil nutrients
Pests & Disease Resistance
Resistance
Good resistance to pink root and downy mildew
Common Pests
Onion maggot, thrips, aphids
Diseases
Purple blotch, downy mildew, white rot
Frequently Asked Questions
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