USDA Hardiness Zone 9b
Frost Dates for 94027 — Atherton, California
Averages from Redwood City, Ca US, the nearest reporting station, 2.5 miles away.
Plant tender crops after January 17, and expect the first autumn freeze around December 12. That leaves about 333 frost-free days.
- Last spring frost
- January 17
- First fall frost
- December 12
- Growing season
- 333 days
- Hardiness zone
- 9b
50% probability
50% probability
frost-free
25 to 30°F annual low
Planting calendar for 94027
| When | What to do |
|---|---|
| November 8 – November 22 | Start peppers and aubergines indoors They need eight to ten weeks under lights before they can go out. |
| November 22 – December 6 | Start tomatoes indoors Six to eight weeks gives a transplant big enough to set fruit early. |
| December 20 – January 3 | Sow peas, spinach, lettuce, radish outdoors These tolerate light frost and prefer to germinate in cool soil. |
| January 17 onward | Transplant tomatoes, peppers, basil, squash, cucumbers The average last freeze has passed — still watch the actual forecast. |
| by September 19 | Sow the autumn crop of carrots, beets and brassicas They need about twelve weeks to size up before growth stops. |
| by November 28 | Harvest tender crops, or be ready to cover them A first freeze two weeks early is well within normal variation. |
| December 12 onward | Plant garlic, mulch beds, lift tender bulbs Garlic wants a cold spell; bare soil loses structure over winter. |
What these dates mean
Wait until after January 17 to put tender plants — tomatoes, peppers, basil, squash — in the ground. That is the date by which half of years in Atherton, California are past their last freeze. Harvest before December 12, which leaves roughly 333 frost-free days.
ZIP 94027 sits in USDA hardiness zone 9b, meaning the average coldest night of the year falls between 25 to 30°F. Zone decides what survives the winter; frost dates decide when to plant each spring. They are different questions, and a plant can pass one and fail the other.
These are thirty-year NOAA averages for 1991–2020, not a forecast. Any individual year can frost two to three weeks either side of these dates, so check the actual forecast before planting out.