Frost Dates: First and last frost dates for Seneca, OR
ℹ️ How to read these charts for the spring
As spring unfolds, the risk of frost gradually decreases each day until your tender plants are finally safe. The probabilities shown in the chart help you make smart decisions about when to plant.
While frost typically forms at 32°F, tender plants can be damaged even when temperatures are slightly higher. Air temperatures are often measured several feet above the ground, but temperatures at plant level can be several degrees colder. Protected areas like porches help by blocking radiational cooling. Given these variables, we consider 36°F the "caution zone" for frost-sensitive plants.
Key dates for your spring planting:
- By August 4, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
- Around July 26, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
- Before July 20, there's still an 80% risk of frost — too early for tomatoes and other tender plants unless you're prepared to protect them
If the 10-day forecast shows no temperatures below 40°F, you might safely plant earlier than the above dates suggest. Many gardeners watch for this weather window to get a head start on the growing season.
| Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| Last 16° | May 1 | Apr 24 | Apr 19 | Apr 15 | Apr 11 | Apr 7 | Apr 3 | Mar 29 | Mar 22 |
| Last 20° | Jun 2 | May 23 | May 16 | May 10 | May 4 | Apr 29 | Apr 23 | Apr 16 | Apr 6 |
| Last 24° | Jul 5 | Jun 24 | Jun 16 | Jun 9 | Jun 2 | May 27 | May 20 | May 12 | May 1 |
| Last 28° | Jul 25 | Jul 17 | Jul 12 | Jul 7 | Jul 3 | Jun 28 | Jun 24 | Jun 18 | Jun 11 |
| Last 32° | Aug 1 | Jul 28 | Jul 25 | Jul 23 | Jul 20 | Jul 18 | Jul 15 | Jul 12 | Jul 8 |
| Last 36° | Aug 4 | Aug 1 | Jul 30 | Jul 28 | Jul 26 | Jul 24 | Jul 23 | Jul 20 | Jul 17 |
ℹ️ How to read these charts for the fall
As summer ends in Seneca, OR, nighttime temperatures begin to drop, and your risk of frost increases with each passing day. Knowing when to expect frost helps you harvest sensitive crops and extend your growing season with protection methods.
The chart below shows the probability of experiencing specific temperatures on various dates. Here's what this means for your garden:
These probabilities help you time your end-of-season harvests and know when to apply protective measures like row covers, cloches, or cold frames to extend your harvest.
| Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| First 16° | Sep 9 | Sep 16 | Sep 21 | Sep 25 | Sep 29 | Oct 3 | Oct 7 | Oct 12 | Oct 19 |
| First 20° | Sep 1 | Sep 6 | Sep 9 | Sep 12 | Sep 15 | Sep 18 | Sep 21 | Sep 25 | Sep 30 |
| First 24° | Aug 16 | Aug 22 | Aug 26 | Aug 30 | Sep 2 | Sep 5 | Sep 9 | Sep 13 | Sep 18 |
| First 28° | Aug 5 | Aug 10 | Aug 14 | Aug 18 | Aug 21 | Aug 24 | Aug 27 | Aug 31 | Sep 6 |
| First 32° | Jul 30 | Aug 1 | Aug 4 | Aug 6 | Aug 8 | Aug 10 | Aug 12 | Aug 14 | Aug 18 |
| First 36° | Jul 31 | Aug 1 | Aug 2 | Aug 2 | Aug 3 | Aug 4 | Aug 4 | Aug 5 | Aug 7 |
📍 Frost Dates for other nearby locations
- John Day, OR 19.8 mi
- Long Creek, OR 40.8 mi
- Austin, OR 45.2 mi
- Drewsey, OR 47.3 mi
- Monument, OR 56.2 mi
- Unity, OR 58.3 mi
- Beulah, OR 59.2 mi
- Malheur Refuge Hq, OR 61.1 mi
- O O Rch, OR 63.8 mi
- Squaw Butte-northern Great Bas, OR 68.4 mi
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Data is provided by the NOAA National Centers for Environmental Information.