In zone 7, plant onion transplants or sets outside from about March 20, roughly four weeks before your last spring frost. To grow your own transplants, start seeds indoors from January 9 to January 23. Intermediate-day onions are the most reliable choice for zone 7.
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 7
| Task | When |
|---|---|
| Start indoors | January 9 – January 23 |
| Transplant outside | March 20 |
| First harvest | June 18 – August 7 |
| Thin or space plants | About 3 inches apart for full-size bulbs |
| Side-dress | When plants have 5–6 leaves |
| Cure | About 2 weeks in a dry, airy, shaded place |
Most of zone 7 sees its last spring frost between April 10 and April 26, with a typical date of April 17. 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 7
Onions start forming bulbs when days reach a certain length. Zone 7 sits in the middle of the country, where intermediate-day onions, which bulb at 12–15 hours of daylight, are the most reliable. Long-day types also work in the northern part of the zone.
- Intermediate-day varieties: Candy, Superstar, Sierra Blanca, Cimarron, Utopia and Fuego (red).
- Long-day varieties for northern parts of the zone: Yellow Sweet Spanish and Southport Red Globe.
- Choose varieties under 100 days to maturity so bulbs finish before midsummer heat.
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 7 onion tips
- Plant early in spring. Onions handle cold well, and bigger plants make bigger bulbs.
- Don’t plant into warm soil. Soil above 75 °F can make onions bolt before they bulb.
- Feed in two steps. Work fertilizer into the soil before planting, then side-dress when plants have five or six leaves.
- Water lightly and often, and stop once the tops begin to fall over so the bulbs can mature.
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 7 in April?
It is late for full-size bulbs, because plants won’t be big when bulbing starts. You can still plant for green onions.
Which onions grow best in zone 7?
Intermediate-day onions are the most reliable in the middle latitudes. Long-day onions also do well in the northern part of the zone.
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.