USDA Hardiness Zone 9b
Frost Dates for 92508 — Riverside, California
Averages from Riverside Fire Stn 3, Ca US, the nearest reporting station, 5.7 miles away.
Plant tender crops after January 9, and expect the first autumn freeze around December 25. That leaves about 353 frost-free days.
- Last spring frost
- January 9
- First fall frost
- December 25
- Growing season
- 353 days
- Hardiness zone
- 9b
50% probability
50% probability
frost-free
25 to 30°F annual low
Planting calendar for 92508
| When | What to do |
|---|---|
| October 31 – November 14 | Start peppers and aubergines indoors They need eight to ten weeks under lights before they can go out. |
| November 14 – November 28 | Start tomatoes indoors Six to eight weeks gives a transplant big enough to set fruit early. |
| December 12 – December 26 | Sow peas, spinach, lettuce, radish outdoors These tolerate light frost and prefer to germinate in cool soil. |
| January 9 onward | Transplant tomatoes, peppers, basil, squash, cucumbers The average last freeze has passed — still watch the actual forecast. |
| by October 2 | Sow the autumn crop of carrots, beets and brassicas They need about twelve weeks to size up before growth stops. |
| by December 11 | Harvest tender crops, or be ready to cover them A first freeze two weeks early is well within normal variation. |
| December 25 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 9 to put tender plants — tomatoes, peppers, basil, squash — in the ground. That is the date by which half of years in Riverside, California are past their last freeze. Harvest before December 25, which leaves roughly 353 frost-free days.
ZIP 92508 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.