When to plant onions in Pennsylvania
Pennsylvania’s average last spring frost is May 1, and the first fall frost typically arrives around October 10 — about 162 frost-free days (USDA zones 5a, 5b, 6a, 6b, 7a, 7b). Onion needs 90–120 days to mature, which fits comfortably within Pennsylvania's growing season.
Pennsylvania covers a wide range of climates, so your exact frost dates may differ from the state average by two weeks or more. For dates tuned to your town, use the calendar generator.
When to plant onions in Pennsylvania: the short answer
For a spring planting, plant out Apr 3 – Apr 20, with seeds started indoors Feb 13 – Feb 27. Seeds germinate in soil from 40 to 90°F.
Windows are ~1–2 week bands around each date. Frost dates are a statewide average from NOAA/NCEI normals; your town may differ by two weeks or more. Calendar year 2026.
How to grow onions in Pennsylvania, step by step
- Start seeds indoors (Feb 13 – Feb 27). Sow seeds ½ inch deep in seed-starting mix under bright light. They take 7-14 days to sprout, fastest in soil around 70°F. Harden seedlings off for a week before they go outside.
- Prepare the bed. They need at least six to eight hours of direct sun a day and loose soil at least 12 inches deep, with a pH between 6.0 and 7.0. Dig in compost before planting.
- Plant out (Apr 3 – Apr 20). Space plants about 4 inches apart in rows 12 inches apart. It handles frost well, so it can go out before the last frost date. As a cool-season crop it does best before summer heat arrives in Pennsylvania.
- Water and feed. Give it steady, even moisture, about an inch of water a week from rain or the hose.
- Watch for pests and problems. Pests: onion maggot, onion thrips. Diseases and disorders: downy mildew, white rot, neck rot, purple blotch.
- Harvest (from about Jul 9 – Aug 8). Onion takes 90-120 days to reach harvest. Match the day-length type to your latitude: long-day onions for the north, short-day for the south, day-neutral anywhere. Bulbing is triggered by day length, not calendar date.
Figures come from our crop data; dates use Pennsylvania’s average frost dates. More in the full onion growing guide.
Onion planting dates by USDA zone in Pennsylvania
Pennsylvania spans USDA zones 5a, 5b, 6a, 6b, 7a, 7b. Colder zones, usually higher or further inland, have a later last spring frost and an earlier first fall frost than the state average, so the onion dates shift with them.
When to plant onions in nearby states
| State | Last frost | Plant out |
|---|---|---|
| Pennsylvania (this page) | May 1 | Apr 3 – Apr 20 |
| New Jersey | April 20 | Mar 23 – Apr 9 |
| Delaware | April 14 | Mar 17 – Apr 3 |
| Maryland | April 14 | Mar 17 – Apr 3 |
| District of Columbia | April 10 | Mar 13 – Mar 30 |
| Virginia | April 15 | Mar 18 – Apr 4 |
| West Virginia | May 5 | Apr 7 – Apr 24 |
Questions gardeners in Pennsylvania ask
When is the best time to plant onions in Pennsylvania?
Plant onion transplants outdoors in Pennsylvania between April 3 and April 20. That timing is set by Pennsylvania's average last spring frost of May 1; Pennsylvania spans several climates, so cooler and higher parts of the state run later.
When should I start onion seeds indoors in Pennsylvania?
Start seeds indoors between February 13 and February 27, about 10 weeks before the last frost, so the seedlings are ready to plant out from April 3.
When will onions planted in Pennsylvania be ready to harvest?
Planted on time, onions are usually ready from about July 9 to August 8, 90-120 days after transplanting.
When is the last frost in Pennsylvania?
On average around May 1, with the first fall frost around October 10 - about 162 frost-free days. Your town may differ by two weeks or more.