Growing Onions in Ohio
Ohio’s climate is well-suited for growing cold-season vegetables—onions are on the list. Whether from seeds sowed directly into the garden or seedlings to be transplanted, spring time is best for growing most onion varieties.
Onions are biennials—they produce seeds in their second year. Bulbs typically have green, brown, red, or yellow skins. They are round, flat, or elongated. Green onions (scallions) are harvested when they are small and immature.
Short-day, Intermediate or Long-day
Onions are grown in U.S. Department of Plant Hardiness Zones 3 to 9. Short-day and intermediate types are recommended for Ohio’s zones of 5 and 6; plant them before the long, hot days of summer. You can grow a variety of onions—depending on your garden’s soil pH, temperature, and location.
Photoperiod—or the length of time that sunlight affects growing vegetation—is part of what encourages onions (and all plants) to develop. Short-day onion bulbs form when days have 12 or fewer hours of sunlight. Long-day varieties grow when there are 15 (or more) hours of daylight. Intermediate … somewhere in between. Because of limited amounts of direct sunlight, some onion cultivars won’t grow well in Northern Ohio; their bulbs start to form before the plants can sustain them.
When started in late summer, Egyptian onions (Allium cepa var. viviparum) spur clusters of small bulbs—bulbils—on top of the stalks. (Green onions have these small bulbils at their roots). Because Egyptian onions grow in autumn, they can live through most normal winter conditions (with mulch protection) and then be harvested in spring.
Sweet yellow and white Spanish onion globes (Allium cepa) are popular choices for home gardens; they thicken and spread underground during the growing season. Other short-day varieties are available in sets or started indoors by seeds.
- “Red” (Allium cepa ‘red’)
- “Bermuda” (Allium cepa ‘Bermuda’)
- “Walla Walla” (Allium cepa ‘Walla Walla’)
- “Vidalia” (Allium cepa ‘Vidalia’)
- “Egyptian” Egyptian (Allium cepa var. viviparum)
Also called winter onions (and not as tender as other varieties), Egyptian onions are very cold-hardy, however, you cannot start them from seeds; they sprout bulbils at the top of the plants.
Check out these types: Green; White Portugal; Ebenezer; Beltsville; Yellow Globe; White Spear; Stuttgarter; Tokyo Long White; and Elite.
Frost dates are figured as average numbers of days between the first and last freeze of the spring and fall seasons. This range is not a scientific declaration, per se, but allows gardeners to use specific guidelines for when to plant and harvest.
Northern Ohio is in USDA hardiness zone 5, where temperatures don’t typically fall below 15 degrees below zero (Fahrenheit). If you live in the Cleveland area or other sections of the “North Coast,” March to early April is usually a good time to plant—but not always. The best rule of (green) thumb is to plant onion seedlings into the ground after the danger of frost has passed; usually by mid-April but it could be as late as mid-May.
Average Frost Dates in Ohio
Last Frost Date
First Frost Date
Starting Onions Indoors
Onions grow in direct sunlight. Plant the seeds indoors; about ¼ inch deep in fertile soil. Water daily but be careful not to over-soak them. The seeds will germinate in 4 to 10 days. When embedding onion seedlings into your garden, be sure to avoid areas where weeds tend to grow; the tiny plants can suffocate easily.
In Ohio, testing the garden soil before applying any kind of fertilizer is recommended; you can do so through your county extension service or the purchase of a specially-designed kit. Fertilizing mixtures of a 1-2-2 ratio (NPK; nitrogen, phosphorus, and potassium) typically work well for onions. Organic fertilizers are also suitable; the ratios vary.
Disease and Pests
Onions are susceptible to viral, bacterial and fungal diseases. Disease and fungal growth might include Fusarium basil rot, Botrytis, and white rot. Rotating the crops at different planting intervals should help to prevent these diseases. Planting in clean, well-draining soil is recommended. Thrips, downy mildew, maggots, smut, and pink root are diseases to look for; garden bugs and weeds must be kept under control.
Facts About Onions
- Onions are started by seeds, sets and transplants. Garden stores offer sets for transplanting—arguably the easiest way to grow onions. Sets, which are onion bulbs previously started from seeds, are small and firm.
- Onions grow in soil temperatures of 36 degrees Fahrenheit or higher (they thrive in climates where the temps are 50 F. or more). Plant the greenery when the temperatures are at 55 to 75 degrees F. Onions are generally frost-tolerant.
- For the developing bulbs to spread, space the plants about 6 inches apart and 2 inches deep.
- Water as needed so that roots grow downward. Light mulching will help protect moisture from dissipating.
- Onions are ready for harvesting when tops have fallen over. Bulb skin will be paper-like.
- Eat onions when they’re green or fully mature.
Reap and Store
Sweet onions grown in the Buckeye State are freshest when eaten promptly, but you can cure and store them for future use. Mature bulbs have the tops falling over—they’re ready to be picked!
Set onions in a warm, dry area (away from direct sunlight) for 10 to 14 days; the location should have low humidity and good air circulation. When the onions have their papery dry skin, remove the roots and tops. Place onions in containers with punch holes but NOT in plastic bags where air cannot circulate.
Store cured onions in temperatures of 32 to 45 degrees F; they can be loose, in mesh bags, or tied into braided strings and suspended. If kept in a basement or root cellar, onions may last up to six or eight months.
Questions & Answers
© 2018 Teri Silver