When to plant · 13 cities · zones 6b–7b
When to plant onions in Pennsylvania
Start Spanish Onion seeds indoors around Feb 2 and transplant around Mar 30 — the Pennsylvania statewide median, counted from a last spring frost of Apr 27 across 1,833 ZIP codes and 179 NOAA stations.
The rule: Twelve weeks indoors, the earliest sowing on the calendar, then transplant about four weeks before the last frost.
Pennsylvania onions, by step
Statewide median last frost Apr 27, first fall frost Oct 20, 2027 season. Each cultivar's own indoor lead time and days to maturity, same engine as the Plan Builder.
| Cultivar | Start indoors | Plant out | First harvest | Days |
|---|---|---|---|---|
| Spanish OnionYellow Sweet Spanish (long-day) | Feb 2 | Mar 30 | Jul 18 | 110 from transplant |
Tight means first harvest lands within two weeks of the median first fall frost. Statewide dates are the ZIP-weighted median of every NOAA 1991–2020 station Pennsylvania's ZIP codes resolve to.
Onions in Pennsylvania, city by city
Spanish Onion, scheduled from each city's nearest NOAA station — the same dates as its frost page.
| City | Last frost | Start indoors | Plant out | First harvest |
|---|---|---|---|---|
| Philadelphiazone 7b | Mar 30 | Jan 5 | Mar 2 | Jun 20 |
| Pittsburghzone 6b | Apr 18 | Jan 24 | Mar 21 | Jul 9 |
| Allentownzone 7a | Apr 20 | Jan 26 | Mar 23 | Jul 11 |
| Readingzone 7a | Apr 14 | Jan 20 | Mar 17 | Jul 5 |
| Eriezone 7a | Apr 26 | Feb 1 | Mar 29 | Jul 17 |
| Bethlehemzone 7a | Apr 20 | Jan 26 | Mar 23 | Jul 11 |
| Scrantonzone 6b | Apr 23 | Jan 29 | Mar 26 | Jul 14 |
| Lancasterzone 7a | Apr 19 | Jan 25 | Mar 22 | Jul 10 |
| Harrisburgzone 7a | Apr 15 | Jan 21 | Mar 18 | Jul 6 |
| Yorkzone 7a | Apr 26 | Feb 1 | Mar 29 | Jul 17 |
| Wilkes-Barrezone 7a | Apr 23 | Jan 29 | Mar 26 | Jul 14 |
| Altoonazone 6b | Apr 25 | Jan 31 | Mar 28 | Jul 16 |
| State Collegezone 6b | Apr 20 | Jan 26 | Mar 23 | Jul 11 |
What these onions become
What Pennsylvania onions need
Yellow Sweet Spanish Onion Seed
A long-day storage onion with enough sugar to sweat down without scorching. The aromatic base under every tomato sauce on this site.
Organic Seed Starter Potting MixMust have
Seed-starting mix is not potting soil with a nicer label — it is finer, lighter, and low in nutrients on purpose, because a seedling's first roots want air and moisture, not fertiliser.
72-Cell Trays with 1020 Bottoms, 5-PackMust have
The cheap black nursery trays crack after one season and flex enough to break roots when you lift them. These do not. Over five seasons the price per use is lower than the throwaways.
T8 Full-Spectrum Grow Lights, 1 ft 4-packMust have
A south window in March delivers a fraction of the light a pepper seedling needs, and the plant tells you by stretching. Two inches of LED above the canopy for 16 hours a day fixes it permanently.
Rapitest Soil Test Kit
In-ground growers are guessing until they test. pH outside 6.0–6.8 locks nutrients out no matter how much fertiliser you add, and no amount of feeding fixes that.
Pure Organic Worm Castings, 15 lb
Not a fertiliser so much as a soil-biology inoculant with a mild nutrient charge. A cup in each planting hole is a cheap, unglamorous improvement you can measure by August.
Garden Harvest Basket with Tool Caddy
A harvest basket that doubles as a colander means the hose rinse happens in the garden, and the dirt stays outside. On a 20-pound tomato day that is a genuine time saving.
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Onions in Pennsylvania: questions
When should I plant onions in Pennsylvania?
Transplant around Mar 30 at the statewide median; across the state that date runs from Mar 17 in the warmest tenth of Pennsylvania's ZIP codes to Apr 12 in the coldest. To cut the freeze risk to one year in ten, count from May 15 instead of the median last frost. Use the city table for your own town.
When do I start onions seeds indoors in Pennsylvania?
Around Feb 2 for Spanish Onion: 12 weeks before the statewide median last frost, on soil held at 65–75 °F.
When is the last frost in Pennsylvania?
The ZIP-weighted median of NOAA 1991–2020 station medians is Apr 27. In the warmest tenth of Pennsylvania's ZIP codes the median last frost falls on or before Apr 14; in the coldest tenth, on or after May 10.
When will Pennsylvania onions be ready to harvest?
Spanish Onion planted on the statewide date is ready around Jul 18: 110 days from transplant.
Which onions grow in Pennsylvania?
Spanish Onion is a long-day onion, correct above roughly 36° N. Every Pennsylvania city listed here is north of that line.
More for Pennsylvania
- When to plant tomatoes
- When to plant peppers
- When to plant tomatillos
- When to plant basil
- When to plant cilantro
- When to plant carrots
- When to plant mustard greens
Onions in every state → · Pennsylvania frost dates → · How frost-date math works →