Plotwright
Home
Onion
Habit (mature) · Colin / Wikimedia Commons · CC BY-SA 3.0
Limited coverage
Onion
Allium cepa
A biennial Allium grown as an annual for its bulb. Day-length sensitive — northern gardens need long-day cultivars; southern gardens need short-day cultivars; intermediate-day cultivars suit zones 6-7. Planted in spring (sets) or fall (over-wintering); harvested in summer when tops fall over. Edible-as-greens at any stage (green onions / scallions).
Review: Source-backed
Edible
Light
Full sun
Water
Moderate water
Mature size
12-24" tall · 4" apart
Hardy in zones
Annual everywhere
Summer heat range
Cool-Hot
cool to hot summers Interim Plotwright tier until the plant AHS range is authored.
Native in Illinois
No
Related products
Sponsored
Heat and sun protection
Shade cloth, shade hoops, cooling mulch, and heat-stress monitoring tools.
Search heat and sun protection on Amazon
Seed starting
Trays, cells, humidity domes, heat mats, grow lights, and seed-starting mix.
Search seed starting on Amazon
Drainage and aeration
Perlite, pumice, raised-bed mix, aerators, and drainage-focused containers.
Search drainage and aeration on Amazon
Transplanting and establishment
Trowels, transplant spades, starter fertilizer, root stimulators, and watering bags.
Search transplanting and establishment on Amazon
Harvest and processing
Harvest baskets, berry bowls, canning gear, drying racks, and kitchen garden tools.
Search harvest and processing on Amazon
Direct sowing
Seeders, row markers, labels, soil thermometers, and light row cover.
Search direct sowing on Amazon
Plotwright may earn a commission from purchases made through these links, at no extra cost to you.
Cold hardiness
This plant is grown as an annual; hardiness zones don't apply.
Heat tolerance
Loading current AHS heat-zone and plant heat-fit data at your coordinates…
Sources & citations
Cite this page
For lesson plans, articles, or research that uses this page. To cite a single upstream fact instead, use its specific source listed below.
Plotwright. (2026, May 17). Onion (Allium cepa). Retrieved 2026, June 5, from https://plotwright.garden/plants/onion
Sources for every fact
Every fact on this page traces to a source. 18 fields cited18 source-backed.
NC State Extension Gardener Plant Toolbox
University extension service
Backs 17 fields
Identity
Summary
Plant type
Light
Moisture
Hardiness
Heat zone
Size
Spacing
Habit
Design roles
Seasonal interest
Growth stages
Lifecycle
Regional guidance
Success tips
Designer notes
Wikimedia Commons
Photo · CC BY-SA 3.0
Backs 1 field
Image
Community photos
The photos above are our reviewed reference set, curated for accuracy.
Plotwright
Climate-aware plant planning — every plant checked against your zone now and in 2050.
support@arteractive.co
© 2026 Plotwright