Onions are planted about four weeks before your last spring frost, and the right variety depends on how far north you garden. Find your zone below, or enter your ZIP code for dates based on the weather station closest to you.
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 planting dates by zone
| USDA zone | When to plant |
|---|---|
| Zone 3 | April 25 |
| Zone 4 | April 18 |
| Zone 5 | April 10 |
| Zone 6 | April 3 |
| Zone 7 | March 20 |
| Zone 8 | March 3 |
| Zone 9 | February 3 |
Not sure of your zone? Look it up by 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.
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.
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.
Frequently asked questions
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.