How to Plant, Grow, and Harvest Onions
Look in a garden catalog and you'll see all sorts of onion varieties. But if you’re just getting started, all you really have to decide is if you want green onions (also known as scallions or bunching onions) or the traditional larger onions, which are sliced for cooking, salads and sandwiches, and if you prefer yellow, red or white varieties.
To get green onions, you can harvest any onion variety early, grow them from small onions called "sets," rather than seeds (which tend not to mature to a large size) or grow a "green" or bunching variety.
You'll also need to determine which varieties will grow where you live. It’s not climate as much as latitude and day length that affect their growth. Your best bet is to check with your cooperative extension or a local nursery for recommendations for the best onions to grow in your area.
As a general guideline, long-day varieties do best in northern latitudes, and short-day varieties do well in southern latitudes. Intermediate varieties can grow well in most areas.
Shallots, which combine the taste of onions with garlic, are grown the same as onions. Also, onions do fine in containers, which is good to know if you're short on gardening space.
When to plant: About a month to a month and a half before the last frost date, once the soil temperature is above freezing (and preferably around 50 degrees Fahrenheit). In mild-winter climates, you can plant again in fall for a spring crop.
Days to maturity: 60 to 160
Light requirement: Full sun, though onions can handle light shade
Water requirement: Regular
Long-day: Ailsa Craig, Early Yellow Globe, Ebenezer, Red Delicious, Redwing, Snow White Hybrid, Southport Globe, Sweet Spanish, Walla Walla Sweet, White White
Intermediate Day: California Early, Candy, Early Red Burger, Long Yellow Sweet Spanish, Stockton varieties, Superstar, Valencia
Short day: Bermuda, Crystal Wax, Granex, Grano, Red Creole, Savannah Sweet, Southern Belle Red, Vidalia
Bunching: Evergreen Long White, Parade, Santa Clause, White Lisbon, White Spear
Shallots: Ambition, Dutch Yellow, Jermar, Jersey, French Red, Gray (considered the best), Prisma, Pikant, Polka, Red Sun
Planting and Care
For the best results for large, mature onions, grow from seeds or set out nursery plants. You can also grow from sets but these may bolt or flower before the onions fully mature. If you do want to grow from sets, look for the smallest bulbs possible.
Cultivate the soil before planting and work in amendments and a fertilizer. If you’re planting in rows, make them 1 1/2 to 2 feet apart.
Sow seeds 1/2 inch deep and 1/2 inch apart. Thin to about an inch apart for scallions and 3 to 4 inches apart for bulbs. Set nursery plants so the bulb tops are about 1 1/2 inches deep and 4 inches apart. Plant scallion sets about 1 to 2 inches apart and 1 to 2 inches deep. For larger bulbs, plant 3 to 4 inches apart and just deep enough that their pointed ends are at surface level.
Shallots should be set with the points about a half inch below the surface of the soil and 4 to 8 inches apart, with rows 2 to 4 feet apart.
Keep the soil moist and remove weeds, taking care not to injure the onion bulbs, which are close to the surface. Problems are few, though thrips, wireworms and downy mildew may be problematic.
Pull up green onions as soon as they reach a usable size.
For large or mature onions, you need to make preparations before the actual harvest. When the foliage of about half of all of the onions you’ve planted has yellowed and dried, push all of the foliage down to the ground. The onions will be ready to harvest about three weeks later, although you can leave them in the ground until you want to use them. Cut off any flower stalks that form.
Once you’ve harvested the bulbs, set them out on newspaper in a dry, shaded spot a few days (for short-day onions) to up to three weeks. Then carefully clean off any dirt and remove almost all of the stems and roots and store in a dark, cool indoor space. Yellow onions generally are the best for storage.
Harvest shallots when the shoots turn yellow and have died. Separate the bulbs and let them dry for about a month in a cool, dry, shaded space. They will keep for about eight months.
"Cool-Season Vegetables: How to Grow Onions" by Marianne Lipanovich originally appeared on Houzz.com, your connection to skilled pest control professionals and more planting guides for cool-season vegetables.