Mount Hamilton, CA frost dates
Last spring frostMay 3median date
First fall frostNov 18median date
Growing season199 daysfrost-free
Hardiness zone9bZone 9b
How Mount Hamilton compares
- In 8 years out of 10, the last spring frost in Mount Hamilton falls between April 7 and June 5, a 59-day window. The first fall frost falls between October 22 and December 12.
- The median last frost is 33 days later than the California median of Mar 31.
- Its 199-day growing season is longer than 34% of the 636 California places with a regular frost season (state median 235 days).
- The last frost is 72 days later than the zone 9b median of Feb 20. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 9b chart.
- The weather station records an average of 45 nights a year at or below 32°F.
- Nearby San Jose, CA, 22 km away, gets only light, occasional frost, a reminder of how much elevation and distance from the coast matter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 7 |
| 50% (median) | May 3 |
| 10% (safe for tender plants) | June 5 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | October 22 |
| 50% (median) | November 18 |
| 90% (late) | December 12 |
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 Mount Hamilton, CA
Mount Hamilton, CA frost dates — last frost May 3, first frost Nov 18, zone 9b. whenisthelastfrost.com
Crop
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Start indoors: Feb 8 to Feb 22Transplant outside: Apr 5 to Apr 19
Start indoors: Feb 22 to Mar 8Transplant outside: May 17 to May 31
Start indoors: Feb 22 to Mar 8Transplant outside: May 17 to May 31
Start indoors: Mar 8 to Mar 22Transplant outside: May 10 to May 24
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 12 to Apr 26Sow outdoors: Apr 5 to May 10Plant for fall: Sep 23 to Oct 21
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 5 to Apr 19Sow outdoors: Apr 5 to Apr 19Plant for fall: Sep 9 to Sep 30
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 19 to May 3Plant for fall: Aug 12 to Sep 2
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 12 to Apr 26Plant for fall: Aug 12 to Sep 2
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 19 to May 3Plant for fall: Aug 12 to Sep 2
Start indoors: Mar 22 to Apr 5Transplant outside: May 24 to Jun 7Sow outdoors: May 24 to Jun 7
Start indoors: Mar 22 to Apr 5Transplant outside: May 10 to May 24
Sow outdoors: Mar 22 to Apr 12Plant for fall: Aug 26 to Sep 16
Sow outdoors: Mar 22 to Apr 12Plant for fall: Sep 23 to Oct 14
Sow outdoors: Mar 29 to May 10Plant for fall: Oct 7 to Oct 28
Start indoors: Apr 5 to Apr 12Transplant outside: May 17 to May 24Sow outdoors: May 10 to May 24Plant for fall: Sep 2 to Sep 16
Start indoors: Apr 5 to Apr 12Sow outdoors: May 10 to May 24Plant for fall: Sep 9 to Sep 23
Start indoors: Apr 5 to Apr 12Sow outdoors: May 10 to May 24
Start indoors: Apr 5 to Apr 12Transplant outside: May 17 to May 31
Sow outdoors: Apr 12 to May 10Plant for fall: Aug 26 to Sep 9
Sow outdoors: Apr 12 to May 10Plant for fall: Sep 9 to Sep 23
Sow outdoors: Apr 12 to May 3
Sow outdoors: Apr 19 to May 17Plant for fall: Sep 9 to Sep 23
Sow outdoors: Apr 19 to May 10Plant for fall: Sep 23 to Oct 14
Sow outdoors: May 10 to May 31Plant for fall: Sep 2 to Sep 16
Sow outdoors: May 10 to May 24
Transplant outside: May 17 to Jun 7
Plant for fall: Nov 4 to Dec 9
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Mount Hamilton, CA
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 8 – Feb 22 | Apr 5 – Apr 19 | — | — |
| Peppers | Feb 22 – Mar 8 | May 17 – May 31 | — | — |
| Eggplant | Feb 22 – Mar 8 | May 17 – May 31 | — | — |
| Tomatoes | Mar 8 – Mar 22 | May 10 – May 24 | — | — |
| Lettuce | Mar 8 – Mar 22 | Apr 12 – Apr 26 | Apr 5 – May 10 | Sep 23 – Oct 21 |
| Kale | Mar 8 – Mar 22 | Apr 5 – Apr 19 | Apr 5 – Apr 19 | Sep 9 – Sep 30 |
| Broccoli | Mar 8 – Mar 22 | Apr 19 – May 3 | — | Aug 12 – Sep 2 |
| Cabbage | Mar 8 – Mar 22 | Apr 12 – Apr 26 | — | Aug 12 – Sep 2 |
| Cauliflower | Mar 8 – Mar 22 | Apr 19 – May 3 | — | Aug 12 – Sep 2 |
| Okra | Mar 22 – Apr 5 | May 24 – Jun 7 | May 24 – Jun 7 | — |
| Basil | Mar 22 – Apr 5 | May 10 – May 24 | — | — |
| Peas | — | — | Mar 22 – Apr 12 | Aug 26 – Sep 16 |
| Spinach | — | — | Mar 22 – Apr 12 | Sep 23 – Oct 14 |
| Radishes | — | — | Mar 29 – May 10 | Oct 7 – Oct 28 |
| Cucumbers | Apr 5 – Apr 12 | May 17 – May 24 | May 10 – May 24 | Sep 2 – Sep 16 |
| Zucchini & Summer Squash | Apr 5 – Apr 12 | — | May 10 – May 24 | Sep 9 – Sep 23 |
| Winter Squash & Pumpkins | Apr 5 – Apr 12 | — | May 10 – May 24 | — |
| Melons & Watermelon | Apr 5 – Apr 12 | May 17 – May 31 | — | — |
| Carrots | — | — | Apr 12 – May 10 | Aug 26 – Sep 9 |
| Beets | — | — | Apr 12 – May 10 | Sep 9 – Sep 23 |
| Potatoes | — | — | Apr 12 – May 3 | — |
| Swiss Chard | — | — | Apr 19 – May 17 | Sep 9 – Sep 23 |
| Cilantro | — | — | Apr 19 – May 10 | Sep 23 – Oct 14 |
| Green Beans | — | — | May 10 – May 31 | Sep 2 – Sep 16 |
| Sweet Corn | — | — | May 10 – May 24 | — |
| Sweet Potatoes | — | May 17 – Jun 7 | — | — |
| Garlic | — | — | — | Nov 4 – Dec 9 |
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 Mt Hamilton, CA weather station, about 1 km away (elevation 4,206 ft (1,282 m)).
Frost dates near Mount Hamilton
- Coyote May 3 · Nov 18
- San Jose Jan 2 · Dec 25
- Morgan Hill Feb 24 · Nov 27
- Milpitas Jan 12 · Dec 22
- New Almaden Feb 2 · Dec 6
- Santa Clara Jan 12 · Dec 22
- Campbell Feb 2 · Dec 6
- San Martin Feb 24 · Nov 27
- Alviso Jan 6 · Dec 23
- Sunnyvale Jan 6 · Dec 23
Frequently asked questions
When is the last frost in Mount Hamilton, CA?
The median last spring frost in Mount Hamilton, CA is May 3. There is still about a 10% chance of frost after June 5, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Mount Hamilton, CA?
The median first fall frost is November 18, with about a 10% chance of frost before October 22.
How long is the growing season in Mount Hamilton, CA?
About 199 days between the median last spring frost and first fall frost.
What planting zone is Mount Hamilton, CA?
Mount Hamilton, CA is in USDA hardiness zone 9b.