VegetableOnion
Imai Early Yellow Onion
Imai Early Yellow Onion is a heirloom selection descended from the classic Senshu Yellow, bred to mature 10-15 days earlier than the original Imai variety. These large, flat globe bulbs develop thick yellow skin and can reach over 8 ounces at maturity, with crisp, mild flesh that works fresh or cooked. Growing to 18-24 inches tall and requiring 150 days from transplant to harvest, this cool-season onion thrives in zones 2-9 and functions as an overwintering variety in zones 5-6, where it responds to lengthening day length to begin bulb formation.
Photo © True Leaf Market
Growing Conditions
USDA Zone
2-9
Sunlight
Full Sun
Water
Moderate
Soil
Well-drained, Fertile Loam, Moderately Rich
Growth Stats
24 in
Height
TypeUpright
Spacing
3
Plant Profile
Sunlight
Full Sun
Water
Moderate
Zones
2-9
Size
24in H x ?in W
Growth
—
Care
Moderate
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Highlights
This is a medium-day length onion bred specifically for earliness without sacrificing size or flavor. The thick, flat globe shape and substantial 8-ounce bulbs deliver the crisp, mild character gardeners love in Senshu-type onions, but you'll harvest weeks sooner than the original Imai. As a cool-season variety with overwintering capability, it offers flexibility across most of North America, and every part of the plant carries onion flavor, so nothing goes to waste from seed to bulb.
Common Uses
Every part of the Imai Early Yellow plant contributes onion flavor to the kitchen. The mature bulbs work beautifully sliced raw in salads, caramelized for soups and braises, or roasted whole. Young green onions harvested early provide fresh onion notes to soups and garnishes. The thick, crisp flesh and mild character mean these bulbs store well through winter, making them dependable for cooks who want fresh onion flavor far beyond harvest season.
Growing Timeline
No timeline data available yet for this variety.
Care Instructions
Start Indoors
Start seeds indoors 6-8 weeks before your last spring frost to produce sturdy transplants ready for the field. Maintain soil temperature around 65-75°F for reliable germination. Thin seedlings or pot them individually so transplants are sturdy and well-rooted before moving outdoors.
Transplant Outdoors
Transplant after your last frost date when soil has warmed and seedlings have developed 2-3 true leaves. Space transplants 3 inches apart with 10 inches between rows. In zones 5-6, you can also transplant in late summer (August-September) for fall planting and spring harvest as an overwintering crop.
Harvesting
Harvest mature bulbs around 150 days after transplanting when the tops begin to yellow and fall over, signaling the bulb has finished growing. The bulbs should feel firm with papery, thick yellow skin. Pull or dig bulbs carefully to avoid bruising, then cure them in a warm, dry, well-ventilated space (ideally 75-85°F) for 2-3 weeks until the skin is completely dry and the neck has sealed. You can also harvest young plants earlier as green onions if you prefer fresh tops to mature bulbs.
Growing Calendar
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Companion Planting
Ecology & Traits
Edible
Scientific Classification
Allium cepa
Family
Amaryllidaceae
Genus
Allium
Growth Habit
Upright
Native Status
L48 (I)
History & Origin
“Imai Early Yellow descends from Senshu Yellow, a Japanese heirloom onion prized for its flat globe shape and exceptional storage life. This particular selection was developed to address a real gardening problem: the original Imai, while excellent, required a long growing season that didn't suit all climates. Breeders shortened the maturity window by 10-15 days while preserving the varietal character that made Senshu Yellow famous. The result is a heirloom that honors its Japanese roots while adapting to the practical needs of North American gardeners, particularly in cooler zones where overwintering onions are essential.”