How to Grow Green Onions

Two kinds of green onion

“Green onion” covers two different plants, and knowing which one you have explains most of what follows.

True bunching onions (Allium fistulosum, also called Welsh or Japanese bunching onions) grow as clumps of straight white shanks with hollow green leaves. Iowa State notes that they don’t normally form a bulb, are very hardy and are among the first plants up in spring. Because they don’t bulb, day length matters little, and Oregon State notes that the leaves regrow after cutting.

Young bulb onions (Allium cepa) pulled early. Clemson points out that any onion variety harvested before it bulbs is a green onion. Texas A&M says you can pull them from pencil thickness until bulbs begin to form. After that they turn into small bulb onions. This is how thinnings from a bulb-onion row get used, and it is the best use for oversized onion sets.

The flavor is the same in both: the green leaves are mild and sweet, and the white base is stronger (Oregon State).

Varieties recommended by region

Extension services name bunching varieties for their own areas:

• Oregon: He-shi-ko, Ishikura and White Lisbon (Oregon State).
• Florida: Evergreen Bunching and White Lisbon Bunching (UF/IFAS).
• South Carolina: Beltsville Bunching and Evergreen Bunching (Clemson).
• Utah: Evergreen White Bunching, described as a good mild green onion (Utah State).
• Tennessee: Evergreen White Bunching, ready in 60 to 70 days, and Ishikura, a long, slender green onion ready in 60 to 65 days (Tennessee Extension).

Evergreen-type bunching onions appear on extension lists from Utah to South Carolina and Florida.

Seed, sets or transplants

Seed is the cheapest way to grow onions (Texas A&M) and the usual way to grow true bunching types. Oregon State waits until the soil is at least 50°F before sowing outdoors. Germination is slow in cold soil and fast in warm soil. Oregon State’s data for onion seed shows about 13 days to emerge at 50°F, 7 days at 59°F and about 4 days at 77°F. Sow 1/4 to 1/2 inch deep and keep the surface moist until the seedlings are up (Maryland). Seed thickly, since you will thin as you harvest. Clemson sows 1 to 2 inches apart in rows 1 to 2 feet apart, and Oregon State’s minimum is 1 inch between plants. Seed can also be started indoors 8 to 10 weeks before your outdoor planting date (Oregon State).

Sets are the quickest route. Clemson says sets and transplants are ready in 6 to 8 weeks. Nebraska Extension explains why sets suit green onions so well. A set has already completed one short growing season, so it tends to flower rather than build a big bulb, which is a drawback for storage onions but doesn’t matter for scallions. Vermont’s planting guide suggests putting larger sets, those bigger than a dime, 1 inch deep and close enough to touch, and saving the small sets for bulbs.

Transplants are bundles of onion seedlings. Clemson recommends sets or transplants in spring for green onions in South Carolina. Space them closely, as with seed.

When to plant

Green onions are hardy and fit almost anywhere in the cool part of the year. In warm regions, planting stops only in the hottest months.

Cold-winter regions. Sow as soon as the soil can be worked and has warmed to about 50°F, and plant sets with your other very hardy crops, a few weeks before the last frost. The dates for your zone above give the window. Don’t stop after one sowing. The University of Rhode Island calendar, built around a mid-May last frost, shows green onion sowings from mid-March into June. Iowa State suggests a second sowing in midsummer, harvested in fall or held over for the following spring. Small sowings every few weeks give a continuous supply rather than one glut.

The Pacific Northwest. Oregon State gives local windows. On the coast, plant January through May for harvests from March to July. In the western valleys, plant March to May, and in the Columbia and Snake River valleys, February to April. In the high central and eastern areas, wait until May or June.

Florida and the Gulf Coast. UF/IFAS lists bunching onions from September through March in North and South Florida, and from August through March in Central Florida. That covers the whole cool season, with a break in the hot late spring and summer.

The low desert. The University of Arizona calendar for the Phoenix area runs green onion sowings from January to mid-April and again from August through December.

Sun, soil and spacing

Green onions are more forgiving than bulb onions. Maryland Extension says they get by on about 5 hours of direct sun, compared with 6 or more for bulbs. Oregon State and Virginia Tech both list part shade as acceptable. That makes them useful for the edge of a bed that loses afternoon sun.

They want fertile, well-drained soil with plenty of organic matter (Oregon State, Virginia Tech). Feed the bed before planting as you would for any onion crop. Maryland Extension’s onion fact sheet, which covers green onions too, rates onions as having a high nutrient requirement. Because you harvest leaves rather than bulbs, spacing can be tight. Maryland thins to 2 inches for green onions, compared with 4 to 8 inches for bulbs.

Watering, mulching and weeds

Onion roots are shallow (Maryland), so the top few inches of soil must stay evenly moist (Oregon State). Utah State notes that drought stress affects onion flavor. Oregon State suggests a mulch of chopped straw or shredded leaves between rows to hold moisture and keep weeds down. Weeding matters because onions compete poorly with weeds (Maryland). Pull weeds by hand or hoe very shallowly so you don’t cut the onion roots (Texas A&M).

Grow onions in a different spot each year. Oregon State lists rotation, along with good spacing and weeding, as a way to limit onion pests and diseases.

Harvesting

Start harvesting once the plants are about 6 inches tall. Oregon State and Maryland use 6 inches, and Clemson waits for 6 to 8. You can harvest in two ways:

• Cut and come again. With bunching onions, cut the leaves you need and let the plant regrow. Oregon State says the leaves come back several times in a season.
• Pull whole plants. Loosen the soil beside the row with a fork first, then lift and trim the roots (Oregon State). Take whole plants when thinning a crowded row, and when harvesting bulb-onion types before they bulb.

Timing from seed varies with variety and season. UF/IFAS gives 50 to 75 days, Utah State says green onions can be pulled as early as 50 days, and Tennessee gives 60 to 70 days for Evergreen White Bunching. The Rhode Island and Arizona calendars allow much longer, 90 to 100 days, so expect the timing to vary with your season and variety.

For storage, rinse, dry and refrigerate the onions in a plastic bag. Oregon State expects about a week of good quality and Clemson up to two. To freeze them for cooking, chop the onions, spread them on a baking sheet until firm, then pack them in a labeled container and use within 4 months (Oregon State).

Perennial patches

Bunching onions can be left in place as a permanent clump. Iowa State notes that Welsh onions are hardy enough to come back early each spring. Two related perennials are also grown mainly for their greens:

• Egyptian walking onions (Allium × proliferum) form small bulbils at the tops of the stalks instead of flowers. As the bulbils get heavy the stalks bend over, the bulbils root, and the patch spreads. Iowa State says to plant bulbs in early spring or bulbils in fall. Maryland Extension spaces them 9 inches apart and grows them chiefly for greens.
• Shallots and multiplier onions also give good green tops. Clemson cuts some shallot leaves at ground level as green onions. For green onions in Virginia, Virginia Tech plants Egyptian and yellow multiplier onion sets in late October or early November.

Growing in pots

Bunching onions are among the best vegetables for a container or a windowsill. Oregon State recommends a pot at least 6 inches deep with drainage holes. Set it outdoors in full or part sun, or indoors by a sunny window, and water often enough that the mix never dries out. Sow thickly, start snipping at 6 inches, and the pot keeps producing.

Problems and fixes

• Thrips. These tiny insects leave silvery streaks on the leaves. Wash them off with a strong spray of water and encourage natural enemies (Utah State).
• Onion maggots. White larvae feed on roots and the base of the plant. Rotate beds and pull infested plants (Utah State).
• Allium leafminer. Larvae tunnel inside the leaves. Rotate and keep the area weeded (Oregon State lists it as a key pest).
• Cutworms and slugs. Oregon State lists both among the main pests of bunching onions. Keep the bed and its edges free of weeds.
• Rust and powdery mildew. Leave space between plants for airflow and don’t grow onions in the same soil year after year (Oregon State).
• Scallions turning into bulbs. That means you planted bulb-onion types and the days have lengthened. Pull them now, or grow true bunching varieties for summer harvests.
• Flower stalks. Nebraska Extension notes that plants from sets often bloom by midsummer. Harvest set-grown onions early and keep fresh sowings coming.

Regional notes

Cold North. Grow green onions from early spring into fall. Overwintered bunching onions are one of the first fresh crops of the year.

Humid South. Grow them in fall, winter and spring, when heat-loving pests are fewer. UF/IFAS warns that anything planted in August or September in Florida faces hot-weather insects and diseases.

Arid West. Mulch and drip irrigation keep the shallow roots moist. In the low desert, sow within the Arizona calendar’s two windows rather than in late spring and early summer.

Warm-winter areas (zones 9-11). Green onions can be sown through most of the cool season, so plan successive sowings rather than one big planting.