West Mifflin, PA planting zone & frost dates
West Mifflin is in USDA hardiness zone 6b. The last spring frost usually comes around May 2 and the first fall frost around October 20, for a growing season of about 170 days.
Planting calendar for West Mifflin
Dates are counted from the average last spring frost (May 2) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Mar 7 – Mar 21 Transplant outdoors: May 9 – May 16 |
| Peppers | Start seeds indoors: Feb 21 – Mar 7 Transplant outdoors: May 16 – May 23 |
| Eggplant | Start seeds indoors: Feb 21 – Mar 7 Transplant outdoors: May 16 – May 23 |
| Broccoli | Start seeds indoors: Feb 21 – Mar 7 Transplant outdoors: Apr 4 – Apr 18 |
| Cabbage | Start seeds indoors: Feb 21 – Mar 7 Transplant outdoors: Apr 4 – Apr 18 |
| Onions (sets) | Plant outdoors: Apr 4 – Apr 18 |
| Peas | Sow outdoors: Mar 21 – Apr 4 |
| Spinach | Sow outdoors: Mar 21 – Apr 4 |
| Lettuce | Sow outdoors: Apr 4 – Apr 18 |
| Carrots | Sow outdoors: Apr 4 – Apr 18 |
| Potatoes | Plant outdoors: Apr 4 – Apr 18 |
| Beans | Sow outdoors: May 9 – May 16 |
| Sweet corn | Sow outdoors: May 9 – May 16 |
| Cucumbers | Sow outdoors: May 9 – May 16 |
| Squash & zucchini | Sow outdoors: May 9 – May 16 |
| Basil | Start seeds indoors: Mar 21 – Apr 4 Transplant outdoors: May 9 – May 16 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 25 (8 weeks before the average first fall frost on Oct 20).
Useful for zone 6b gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Cold frame / mini greenhouse — adds weeks to a short season
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Apr 17 | May 2 | May 20 |
| First 32°F frost in fall is before | Nov 3 | Oct 20 | Oct 1 |
How to read it: in spring there is a 10% chance of a frost after May 20, so that is a safe date for tender plants. In fall there is a 10% chance of frost before October 1. A hard freeze (28°F) usually ends around April 20.
Hardiness zone by ZIP code in West Mifflin
- 15122 zone 6b
- 15123 zone 6b
Nearby cities
- McKeesport zone 6b, last frost May 2
- Munhall zone 6b, last frost Apr 5
- North Versailles zone 6b, last frost Apr 5
- Wilkinsburg zone 6b, last frost Apr 5
- Monroeville zone 6b, last frost Apr 22
- Jefferson Hills zone 6b, last frost Apr 18
- Baldwin zone 6b, last frost Apr 18
- Whitehall zone 6b, last frost Apr 18
Questions
What growing zone is West Mifflin, PA?
West Mifflin is in USDA Plant Hardiness Zone 6b (average extreme winter low -5°F to 0°F), according to the USDA 2023 map.
When is the last frost in West Mifflin?
The average last spring frost (32°F) in West Mifflin is May 2. There is still a 10% chance of frost until May 20.
When can I plant tomatoes in West Mifflin?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 9 – May 16. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Mckeesport, PA (USC00365573), 2.7 km (1.7 mi) from the city center, elevation 226 m, based on 25 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.