Frost dates for 95140Mount Hamilton, CA
The average last spring frost in Mount Hamilton is May 3 and the average first fall frost is November 18, giving a typical growing season of about 197 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 3
- Average first fall frost
- Nov 18
- Growing season
- 197 days
Safer after Jun 5 (1-in-10 risk)
Possible by Oct 22 (1-in-10 risk)
First frost typically in 22 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Apr 28 · May 27 · Jun 18 | Oct 1 · Oct 29 · Nov 23 | 155 days | 100% |
| Frost / freeze (32°F) | Apr 7 · May 3 · Jun 5 | Oct 22 · Nov 18 · Dec 12 | 197 days | 100% |
| Hard freeze (28°F) | Feb 23 · Apr 10 · May 6 | Nov 10 · Dec 7 · Jan 18 | 241 days | 100% |
Planting calendar for Mount Hamilton
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Apr 2 – Jun 8 |
| Tomatoes | Transplant outdoors | May 19 – Jul 29 |
| Peppers | Start seeds indoors | Apr 2 – May 3 |
| Peppers | Transplant outdoors | Jun 2 – Jul 3 |
| Eggplant | Start seeds indoors | Apr 19 – May 18 |
| Eggplant | Transplant outdoors | Jun 2 – Jul 3 |
| Cucumbers | Sow outdoors | Jun 2 – Aug 8 |
| Summer squash | Sow outdoors | May 19 – Jul 3 |
| Winter squash & pumpkins | Sow outdoors | Jun 2 – Jul 3 |
| Snap beans | Sow outdoors | May 19 – Aug 31 |
| Sweet corn | Sow outdoors | May 19 – Jul 29 |
| Watermelon & cantaloupe | Sow outdoors | Jun 2 – Jul 3 |
| Okra | Sow outdoors | May 26 – Jun 18 |
| Peas | Sow outdoors (spring) | Apr 2 – May 18 |
| Potatoes | Plant outdoors (spring) | Apr 2 – Jun 2 |
| Onions | Start seeds indoors (spring) | Feb 19 – Mar 18 |
| Onions | Transplant outdoors (spring) | Apr 19 – May 18 |
| Broccoli | Start seeds indoors (spring) | Mar 15 – Apr 18 |
| Broccoli | Transplant outdoors (spring) | Apr 19 – May 18 |
| Broccoli | Start seeds indoors (fall) | Jul 19 – Jul 29 |
| Broccoli | Transplant outdoors (fall) | Aug 18 – Aug 29 |
| Cabbage | Start seeds indoors (spring) | Mar 5 – Apr 2 |
| Cabbage | Transplant outdoors (spring) | Apr 2 – May 3 |
| Cabbage | Start seeds indoors (fall) | Jul 9 – Aug 8 |
| Cabbage | Transplant outdoors (fall) | Aug 8 – Sep 8 |
| Leaf lettuce | Sow outdoors (spring) | Apr 2 – Jun 18 |
| Leaf lettuce | Sow outdoors (fall) | Aug 8 – Sep 24 |
| Spinach | Sow outdoors (spring) | Mar 26 – May 9 |
| Spinach | Sow outdoors (fall) | Aug 25 – Sep 29 |
| Radishes | Sow outdoors (spring) | Apr 2 – May 23 |
| Radishes | Sow outdoors (fall) | Aug 8 – Oct 9 |
| Kale | Sow outdoors (spring) | Apr 19 – May 9 |
| Kale | Sow outdoors (fall) | Aug 1 – Sep 8 |
| Carrots | Sow outdoors (spring) | May 3 – Jun 18 |
| Carrots | Sow outdoors (fall) | Jul 9 – Aug 24 |
| Garlic | Plant outdoors (fall) | Nov 8 – Dec 9 |
Where these dates come from
ZIP code 95140 is matched to the NOAA station Mt Hamilton, CA, 0.9 km away, at 4,206 ft elevation (676 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Mt Hamilton, CA (used) | 4,206 ft | May 3 | Nov 18 |
| San Jose, CA | 67 ft | Jan 2 | Dec 25 |
| San Jose, CA | 51 ft | Jan 12 | Dec 22 |
| Los Gatos, CA | 365 ft | Feb 2 | Dec 6 |
Frost dates near Mount Hamilton
- San Jose, CA 95135 · last Feb 2, first Dec 6
- Coyote, CA 95013 · last Feb 2, first Dec 6
- Morgan Hill, CA 95038 · last Feb 24, first Nov 27
- Milpitas, CA 95035 · last Jan 12, first Dec 22
- New Almaden, CA 95042 · last Feb 2, first Dec 6
- Santa Clara, CA 95053 · last Jan 12, first Dec 22
- Campbell, CA 95009 · last Feb 2, first Dec 6
- San Martin, CA 95046 · last Feb 24, first Nov 27
Frequently asked questions
- When is the last frost in Mount Hamilton, CA?
- For ZIP code 95140, the average last spring frost (32°F) is May 3, based on NOAA 1991-2020 climate normals for the Mt Hamilton, CA weather station. There is a 1-in-10 chance of a frost after June 5.
- When is the first frost in Mount Hamilton, CA?
- The average first fall frost (32°F) is November 18. There is a 1-in-10 chance of frost by October 22, so tender plants are at risk from that point on.
- How long is the growing season in 95140?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 197 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.