How to Plant Onion Sets in Fall

Fall-planted onion sets give you a jump on the season: they root in autumn, sit mostly dormant through winter and take off in early spring, producing bulbs in late spring to early summer, weeks ahead of spring-planted onions. The keys are choosing an overwintering variety, planting about 4–6 weeks before your ground freezes, and using small sets (roughly dime-sized or smaller) so plants don’t bolt in spring. This works best in USDA zones 5–9; in zones 3–4 it’s risky without heavy mulch. This guide covers which onions overwinter, planting dates by zone, depth and spacing, winter protection and spring care.

Part of our Vegetable Gardening & Raised Beds guide →

In this guide

1. Which Onions Overwinter?
2. When to Plant Onion Sets in Fall by Zone
3. Choosing Good Onion Sets
4. Preparing the Bed
5. How to Plant Onion Sets in Fall
6. Winter Care: Mulch and Frost Heave
7. Spring Care
8. Harvesting Fall-Planted Onions
9. Troubleshooting Fall Onion Sets
10. Frequently Asked Questions

Which Onions Overwinter?

Not every onion is a good candidate for fall planting. Onions bulb in response to day length, and many varieties also bolt (send up a flower stalk) after a period of cold once the plant has reached a certain size. Varieties bred for overwintering are more tolerant of cold and less inclined to bolt after winter.

Type	Examples	Best regions	Notes
Japanese overwintering onions (sets or transplants)	Senshyu Yellow, Radar, Electric (red), Shakespeare	Zones 5–8	Bred for fall planting; harvest late spring to early summer
Short-day onions (transplants or seed)	Texas Grano, Granex types, 1015Y	Zones 7b–10, the South	Planted fall to winter; bulb as days lengthen in spring
Multiplier and potato onions	Yellow potato onion, multiplier onions	Most zones	Very cold hardy; divide into clusters
Shallots	French gray, Dutch yellow	Zones 4–9	Often planted in fall like garlic
Bunching onions	Evergreen Hardy White	Most zones	Grown for green tops, not bulbs

Standard long-day storage onions sold as spring sets in most garden centers (often labeled simply “yellow,” “white” or “red”) are usually best planted in spring in the North. Fall planting them can lead to a crop of flower stalks instead of bulbs. If you’re comparing sets with seeds and transplants in general, see onion sets vs. seeds.

When to Plant Onion Sets in Fall by Zone

The goal is enough time for roots to establish, but not so much top growth that the plants become large enough to be triggered to bolt by winter cold. Aim for about 4–6 weeks of root growth before the soil freezes.

USDA zone	Typical fall planting window	Notes
3–4	Not generally recommended	Try a small test row in mid-September with 4–6 inches of mulch, or plant in spring
5	Mid-September to early October	Mulch heavily after the ground cools
6	Late September to mid-October	Mulch after first hard frost
7	Early October to early November	Light mulch; protect in cold snaps
8	October to November	Short-day transplants often planted through December
9–10	October to January (short-day types)	Overwintering mostly means growing through mild winter

Local first-frost dates and soil freeze timing vary, so adjust for your conditions. Our article on fall vs. spring planting explains how to time fall crops around your frost dates.

Choosing Good Onion Sets

• Size: choose sets roughly 1/2 to 3/4 inch in diameter. Larger sets look like a head start, but they’re more prone to bolting.
• Firmness: sets should be firm and dry, with no soft spots, mold or sprouting.
• Labeling: buy sets labeled for fall or overwintering planting, ideally with the variety named.
• Storage: if you can’t plant right away, keep sets in a cool, dry, ventilated spot.

Sort your sets before planting. Plant the smallest for bulbs, and plant any larger ones closer together to harvest early as green onions before they have a chance to bolt.

Preparing the Bed

Onions need full sun (at least 6–8 hours) and loose, well-drained soil. Drainage matters even more for fall planting, because sets sitting in cold, wet soil all winter are likely to rot. Raised beds are ideal in heavy clay. Work 2 inches of compost into the top 6–8 inches, and aim for a soil pH of about 6.0–7.0.

Go light on nitrogen at fall planting. A modest amount of phosphorus-rich fertilizer or bone meal mixed into the bed helps root growth, but heavy nitrogen in fall pushes leafy top growth you don’t want going into winter. Save most of the feeding for spring. Rotate: avoid planting where onions, garlic, leeks or shallots grew in the last 2–3 years to reduce onion maggot and disease problems.

How to Plant Onion Sets in Fall

1. Mark rows about 12 inches apart, or plant in blocks on a 4- to 6-inch grid in raised beds.
2. Make holes or a furrow 1–2 inches deep. Fall sets can go slightly deeper than spring sets to protect them from frost heave.
3. Set each bulb pointy end up, root plate down, 4–6 inches apart. Use 4 inches for smaller bulbs and 6 inches for larger bulbs.
4. Cover so the tips are just at or slightly below the surface, and firm the soil gently.
5. Water thoroughly to settle soil around the sets, then keep the bed lightly moist, not soggy, until roots establish.

Birds sometimes pull newly planted sets out of the ground. Covering the bed with row cover or netting for the first couple of weeks prevents this.

Winter Care: Mulch and Frost Heave

Once the soil cools and the top few inches start to freeze, usually after your first hard frost, spread 3–4 inches of loose mulch such as straw or shredded leaves over the bed. In zone 5 and colder, go to 4–6 inches. Mulch insulates the soil and keeps it from repeatedly freezing and thawing, which can heave small sets out of the ground.

• Check after thaws. Push any heaved sets back into the soil.
• Don’t water frozen ground. In dry winters in mild zones, water occasionally on warm days when the soil isn’t frozen.
• Use row cover during severe cold snaps in zones 7–8 where plants are green through winter.
• Watch for voles under thick mulch in some areas; they rarely eat onions, but they can tunnel through beds.

Spring Care

As days lengthen and soil warms in late winter or early spring, onions resume growth. That’s your cue to:

• Pull back heavy mulch from around the plants so the soil can warm, leaving a light layer between rows to suppress weeds.
• Feed with nitrogen. Side-dress with a nitrogen fertilizer or compost when growth resumes, and again about 3–4 weeks later. Stop once bulbs begin swelling noticeably.
• Weed carefully. Onions compete poorly with weeds and have shallow roots, so hand-pull or hoe shallowly.
• Water evenly, about 1 inch per week. Consistent moisture during bulbing gives bigger, milder bulbs.
• Remove flower stalks as soon as you see them. Plants that bolt won’t store well; use those onions first.

Some bolting is normal, especially after a winter of temperature swings. If a lot of your plants are flowering, our guide on why onion sets flower explains the causes and how to prevent it next year.

Harvesting Fall-Planted Onions

Overwintered onions are usually ready from late spring to early summer, roughly May through July depending on zone and variety. You can pull some early as green onions any time. For full bulbs, wait until about half the tops have yellowed and flopped over, then:

1. Stop watering for a few days.
2. Pull or lift the bulbs with a fork on a dry day.
3. Cure them in a warm, dry, shaded, airy place for 2–3 weeks until the necks are dry and papery.
4. Trim roots and tops to about an inch.

Overwintering varieties generally don’t store as long as spring-planted storage onions. Plan to use them within a few months, and rely on a spring-planted storage variety for winter keeping. Our guide to curing onions covers drying and storage in detail.

Troubleshooting Fall Onion Sets

• Sets rotted over winter: soil stayed too wet. Use raised beds or improve drainage next year.
• Plants heaved out of the ground: not enough mulch, or planted too shallowly. Replant immediately if roots are still alive.
• Most plants bolted: wrong variety for fall planting, sets too large, or planted too early so plants got big before winter.
• Small bulbs: poor spring feeding, weed competition, uneven watering or a variety mismatched to your day length.
• Yellowing, wilting seedlings in spring: check for onion maggots at the base; rotate beds and use row covers in spring.

Fall onions fit neatly into a broader fall planting plan alongside garlic and cover crops. Our vegetable gardening guide has more on planning a year-round bed rotation.