Knox, PA frost dates
Last spring frostMay 9median date
First fall frostOct 11median date
Growing season155 daysfrost-free
Hardiness zone6aZone 6a
How Knox compares
- In 8 years out of 10, the last spring frost in Knox falls between April 24 and May 24, a 30-day window. The first fall frost falls between September 30 and October 26.
- The median last frost is 12 days later than the Pennsylvania median of Apr 27.
- Its 155-day growing season is longer than 14% of the 1,787 Pennsylvania places with a regular frost season (state median 175 days).
- The last frost is 10 days later than the zone 6a median of Apr 29. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 6a chart.
- The weather station records an average of 155 nights a year at or below 32°F.
- Compared with Pittsburgh, PA, 96 km away, the last frost here is 15 days later than there and the growing season is 31 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 24 |
| 50% (median) | May 9 |
| 10% (safe for tender plants) | May 24 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 30 |
| 50% (median) | October 11 |
| 90% (late) | October 26 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Planting calendar for Knox, PA
Knox, PA frost dates — last frost May 9, first frost Oct 11, zone 6a. whenisthelastfrost.com
Crop
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Start indoors: Feb 14 to Feb 28Transplant outside: Apr 11 to Apr 25
Start indoors: Feb 28 to Mar 14Transplant outside: May 23 to Jun 6
Start indoors: Feb 28 to Mar 14Transplant outside: May 23 to Jun 6
Start indoors: Mar 14 to Mar 28Transplant outside: May 16 to May 30
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 18 to May 2Sow outdoors: Apr 11 to May 16Plant for fall: Aug 16 to Sep 13
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 11 to Apr 25Sow outdoors: Apr 11 to Apr 25Plant for fall: Aug 2 to Aug 23
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 25 to May 9Plant for fall: Jul 5 to Jul 26
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 18 to May 2Plant for fall: Jul 5 to Jul 26
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 25 to May 9Plant for fall: Jul 5 to Jul 26
Start indoors: Mar 28 to Apr 11Transplant outside: May 30 to Jun 13Sow outdoors: May 30 to Jun 13
Start indoors: Mar 28 to Apr 11Transplant outside: May 16 to May 30
Sow outdoors: Mar 28 to Apr 18Plant for fall: Jul 19 to Aug 9
Sow outdoors: Mar 28 to Apr 18Plant for fall: Aug 16 to Sep 6
Sow outdoors: Apr 4 to May 16Plant for fall: Aug 30 to Sep 20
Start indoors: Apr 11 to Apr 18Transplant outside: May 23 to May 30Sow outdoors: May 16 to May 30Plant for fall: Jul 26 to Aug 9
Start indoors: Apr 11 to Apr 18Sow outdoors: May 16 to May 30Plant for fall: Aug 2 to Aug 16
Start indoors: Apr 11 to Apr 18Sow outdoors: May 16 to May 30
Start indoors: Apr 11 to Apr 18Transplant outside: May 23 to Jun 6
Sow outdoors: Apr 18 to May 16Plant for fall: Jul 19 to Aug 2
Sow outdoors: Apr 18 to May 16Plant for fall: Aug 2 to Aug 16
Sow outdoors: Apr 18 to May 9
Sow outdoors: Apr 25 to May 23Plant for fall: Aug 2 to Aug 16
Sow outdoors: Apr 25 to May 16Plant for fall: Aug 16 to Sep 6
Sow outdoors: May 16 to Jun 6Plant for fall: Jul 26 to Aug 9
Sow outdoors: May 16 to May 30
Transplant outside: May 23 to Jun 13
Plant for fall: Sep 27 to Nov 1
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Knox, PA
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 14 – Feb 28 | Apr 11 – Apr 25 | — | — |
| Peppers | Feb 28 – Mar 14 | May 23 – Jun 6 | — | — |
| Eggplant | Feb 28 – Mar 14 | May 23 – Jun 6 | — | — |
| Tomatoes | Mar 14 – Mar 28 | May 16 – May 30 | — | — |
| Lettuce | Mar 14 – Mar 28 | Apr 18 – May 2 | Apr 11 – May 16 | Aug 16 – Sep 13 |
| Kale | Mar 14 – Mar 28 | Apr 11 – Apr 25 | Apr 11 – Apr 25 | Aug 2 – Aug 23 |
| Broccoli | Mar 14 – Mar 28 | Apr 25 – May 9 | — | Jul 5 – Jul 26 |
| Cabbage | Mar 14 – Mar 28 | Apr 18 – May 2 | — | Jul 5 – Jul 26 |
| Cauliflower | Mar 14 – Mar 28 | Apr 25 – May 9 | — | Jul 5 – Jul 26 |
| Okra | Mar 28 – Apr 11 | May 30 – Jun 13 | May 30 – Jun 13 | — |
| Basil | Mar 28 – Apr 11 | May 16 – May 30 | — | — |
| Peas | — | — | Mar 28 – Apr 18 | Jul 19 – Aug 9 |
| Spinach | — | — | Mar 28 – Apr 18 | Aug 16 – Sep 6 |
| Radishes | — | — | Apr 4 – May 16 | Aug 30 – Sep 20 |
| Cucumbers | Apr 11 – Apr 18 | May 23 – May 30 | May 16 – May 30 | Jul 26 – Aug 9 |
| Zucchini & Summer Squash | Apr 11 – Apr 18 | — | May 16 – May 30 | Aug 2 – Aug 16 |
| Winter Squash & Pumpkins | Apr 11 – Apr 18 | — | May 16 – May 30 | — |
| Melons & Watermelon | Apr 11 – Apr 18 | May 23 – Jun 6 | — | — |
| Carrots | — | — | Apr 18 – May 16 | Jul 19 – Aug 2 |
| Beets | — | — | Apr 18 – May 16 | Aug 2 – Aug 16 |
| Potatoes | — | — | Apr 18 – May 9 | — |
| Swiss Chard | — | — | Apr 25 – May 23 | Aug 2 – Aug 16 |
| Cilantro | — | — | Apr 25 – May 16 | Aug 16 – Sep 6 |
| Green Beans | — | — | May 16 – Jun 6 | Jul 26 – Aug 9 |
| Sweet Corn | — | — | May 16 – May 30 | — |
| Sweet Potatoes | — | May 23 – Jun 13 | — | — |
| Garlic | — | — | — | Sep 27 – Nov 1 |
Dates come from the median frost dates and common extension-service timing. Adjust for your soil temperature, microclimate and the varieties you grow.
About these dates
Based on 1991–2020 NOAA climate normals for the Clarion 3 Sw, PA weather station, 8 km away (elevation 1,040 ft (317 m)).
Frost dates near Knox
- Curllsville May 9 · Oct 11
- Limestone May 9 · Oct 11
- Shippenville May 9 · Oct 11
- Kossuth May 9 · Oct 11
- Turkey City May 9 · Oct 11
- Lamartine May 9 · Oct 11
- Callensburg May 9 · Oct 11
- Clarion May 9 · Oct 11
- Sligo May 9 · Oct 11
- Marble May 9 · Oct 11
Frequently asked questions
When is the last frost in Knox, PA?
The median last spring frost in Knox, PA is May 9. There is still about a 10% chance of frost after May 24, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Knox, PA?
The median first fall frost is October 11, with about a 10% chance of frost before September 30.
How long is the growing season in Knox, PA?
About 155 days between the median last spring frost and first fall frost.
What planting zone is Knox, PA?
Knox, PA is in USDA hardiness zone 6a.