Frost Dates: First and last frost dates for Mt Hamilton, CA
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 June 17, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
- Around May 29, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
- Before May 17, 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° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| Last 20° | Feb 6 | Jan 21 | Jan 6 | Dec 15 | -- | -- | -- | -- | -- |
| Last 24° | Apr 14 | Mar 26 | Mar 13 | Feb 28 | Feb 15 | Feb 1 | Jan 10 | -- | -- |
| Last 28° | May 14 | May 3 | Apr 26 | Apr 19 | Apr 13 | Apr 7 | Mar 31 | Mar 23 | Mar 13 |
| Last 32° | Jun 6 | May 27 | May 20 | May 14 | May 8 | May 2 | Apr 26 | Apr 19 | Apr 9 |
| Last 36° | Jun 17 | Jun 10 | Jun 6 | Jun 2 | May 29 | May 26 | May 22 | May 17 | May 11 |
ℹ️ How to read these charts for the fall
As summer ends in Mt Hamilton, CA, 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° | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| First 20° | Dec 9 | Dec 28 | Jan 16 | -- | -- | -- | -- | -- | -- |
| First 24° | Nov 16 | Dec 5 | Dec 19 | Jan 2 | Jan 16 | Feb 2 | Mar 4 | -- | -- |
| First 28° | Nov 7 | Nov 17 | Nov 25 | Dec 1 | Dec 7 | Dec 13 | Dec 19 | Dec 26 | Jan 6 |
| First 32° | Oct 19 | Oct 28 | Nov 4 | Nov 10 | Nov 15 | Nov 20 | Nov 26 | Dec 3 | Dec 12 |
| First 36° | Oct 7 | Oct 14 | Oct 19 | Oct 23 | Oct 27 | Oct 31 | Nov 4 | Nov 9 | Nov 15 |
📍 Frost Dates for other nearby locations
- San Jose, CA 19.5 mi
- Los Gatos, CA 23.2 mi
- Gilroy, CA 24.1 mi
- Livermore, CA 25.8 mi
- Newark, CA 29.5 mi
- Watsonville Wtr Wks, CA 29.8 mi
- Tracy Carbona, CA 31.2 mi
- Tracy Pumping Plt, CA 31.8 mi
- Santa Cruz, CA 34.2 mi
- Palo Alto, CA 35.1 mi
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Data is provided by the NOAA National Centers for Environmental Information.