In zone 5, plant onion transplants or sets outside from about April 10, roughly four weeks before your last spring frost. To grow your own transplants, start seeds indoors from January 30 to February 13. Grow long-day onions, which form bulbs in the long days of a northern summer.
Onion dates for your ZIP code
Planting times based on university extension guidance (UNH, Cornell, Purdue, Minnesota, Nebraska and UMass Extension). Frost dates from NOAA 1991–2020 U.S. Climate Normals, nearest weather station. Zones derived from the 2023 USDA Plant Hardiness Zone Map data (PRISM Climate Group, Oregon State University). This is not the official USDA Plant Hardiness Zone Map.
Onion timing in zone 5
| Task | When |
|---|---|
| Start indoors | January 30 – February 13 |
| Transplant outside | April 10 |
| First harvest | July 9 – August 28 |
| Thin or space plants | 4–5 plants per foot of row |
| Stop watering | When the tops start to fall over |
| Cure | About 2 weeks in a dry, airy, shaded place |
Most of zone 5 sees its last spring frost between May 2 and May 17, with a typical date of May 8. Onions tolerate frost and temperatures well below freezing, so they are among the first crops planted in spring. The tool above uses the weather station closest to your ZIP code.
Why the type of onion matters
Onions form bulbs when the days reach a certain length, and different varieties respond to different day lengths. Short-day onions bulb at 10–12 hours of daylight and suit the South. Intermediate-day onions bulb at 12–15 hours and suit the middle latitudes. Long-day onions need 14–16 hours and suit the North. Planting the wrong type is the most common reason onions stay small.
Best onion varieties for zone 5
Onions start forming bulbs when the days reach a certain length, so the right type depends on where you live. In zone 5, which covers the northern states, grow long-day onions. They need 14–16 hours of daylight to bulb, which northern summers provide.
- Long-day varieties: Yellow Sweet Spanish, Downing Yellow Globe, Ebenezer, Southport White Globe and Southport Red Globe.
- Avoid short-day onions. Bred for southern winters, they bulb too early here and stay small.
How to plant onions
- Choose sets, transplants or seed. Sets and transplants are easiest and give the biggest bulbs in a short season.
- Plant early, about four weeks before your last spring frost. Onions tolerate cold well.
- Plant shallow: about ¾ inch deep and never deeper than 1 inch, 3–4 inches apart.
- Fertilize before planting, then side-dress when plants have five or six leaves.
- Water lightly and often, keeping the soil evenly moist.
Zone 5 onion tips
- Use sets or transplants. In short-season areas they produce larger bulbs than seed sown in the garden.
- Plant early. The bigger the plant when long days arrive, the bigger the bulb.
- Water lightly and often. Onion roots rarely go deeper than 18 inches, so frequent light watering works better than occasional soaking.
- Don’t overfeed. Onions need fertile soil, but high rates of nitrogen are not helpful.
Harvesting and curing onions
Onions are ready when the necks weaken and the tops fall over. Once a quarter to half of the tops are down, lift the bulbs and lay the tops over them to prevent sunburn. Dry them in a shaded, well-ventilated place for about two weeks, then cut off the tops and store the bulbs in mesh bags or slatted boxes somewhere cool and dry. Green onions can be picked any time once they are pencil-size.
Onion planting dates in nearby zones
See dates for every zone on the onions planting guide, or build a full schedule with the planting calendar.
Frequently asked questions
Is it too late to plant onions in zone 5 in May?
It is late for bulbs. Onions planted in May have little time to grow before the long days trigger bulbing, so the bulbs will be small. Green onions are still worth planting.
Should I plant onion sets or transplants in zone 5?
Either works, and both give larger bulbs than seed sown directly in the garden in a short season. Transplants usually make bigger, better-keeping bulbs.
Can onions handle frost?
Yes. Onions are a cool-season crop and tolerate temperatures well below freezing, so they are planted about four weeks before your last spring frost.
How deep should I plant onions?
About ¾ inch deep for sets and transplants, and never deeper than 1 inch. Seeds go ¼ inch deep.
What is the difference between short-day and long-day onions?
Short-day onions start bulbing at 10–12 hours of daylight and suit the South. Long-day onions need 14–16 hours and suit the North. Intermediate types fall in between.
Sources. Planting dates use the median frost dates of each USDA zone, calculated from NOAA climate data for every ZIP code in the zone.