Frost dates for Riverside, California
Riverside doesn't get a freezing night every winter: about 58 years in 100 have one. In those years, half have had their last frost by January 9 and half their first by December 30.
Frost dates for
Riverside, California
Last spring frost
January 9
Not every winter has one: about 58 years in 100 have a freezing night here. In those years, half have their last frost by this date, and 1 in 10 still have one after February 21.
First fall frost
December 30
In years with a freeze, half have their first one by this date, and 1 in 10 by December 5.
Growing season
362 days
Frost-free days in a typical year. 9 years in 10 get at least 319.
Hardiness zone
10a
2023 USDA map: the coldest night of winter averages 30°F to 35°F. On the 2012 map it was 9b, half a zone colder. ZIP codes within about 6 miles of the city's center: 1 in 9b and 8 in 10a.
Stations near you disagree. NOAA's Riverside Municipal Airport (3 miles away, at 800 feet above sea level), the one we used, gives a typical last frost of January 9 and a typical first frost of December 30. NOAA's Redlands (15 miles away, at 1,410 feet above sea level) gives a typical last frost of January 27 and a typical first frost of December 19. So the typical last frost could fall anywhere from January 9 to 27 and the typical first frost from December 19 to 30, depending on whether your garden is more like one or the other. Local terrain matters: hillsides, valley floors, water and city heat can change frost dates a lot over a few miles. Treat the dates here as a starting point, and compare with a nearby gardener or your county extension office.
Print a year planner for Riverside
Frost risk through the year
How sure are these dates?
A frost date is a probability, not a promise. NOAA worked out, from 30 years of nightly lows, how often the last spring frost and the first fall frost fall on each date. The middle column is the typical year. The outer columns are the early and late years that come about once a decade.
| Early year 1 in 10 | Typical year 1 in 2 | Late year 1 in 10 | |
|---|---|---|---|
| Last frost in spring | December 16 | January 9 | February 21 |
| First frost in fall | December 5 | December 30 | February 6 |
The frost-free season between them runs 362 days in a typical year. In 1 year in 10 there is no freeze at all, and in 1 year in 10 it is 319 days or shorter.
- Frost possible (36°F at the station): about 98 years in 100 have one. In those years the last typically comes on February 13 and the first on December 12. On clear, still nights the ground can be several degrees colder than the thermometer, so frost can form on plants when the official reading is in the mid-30s.
Planting calendar for Riverside
These dates count from the typical last and first frosts, using the planting rules published by Colorado State University Extension (spring), Virginia Cooperative Extension (fall crops) and University of Minnesota Extension (garlic, where winters are hard). Weather in any one year can run early or late, so check the forecast before you plant tender crops.
Frost doesn't come every year here: about 58 years in 100 have at least one freezing night. The calendar is built on the dates for the years that do.
We don't give a garlic date here. The rule we use, from the University of Minnesota Extension, counts from the first killing frost, and it works where a hard freeze comes every year before the ground freezes. Your county's extension office can tell you when to plant garlic in your climate.
Your typical last frost comes before mid-February. Where winters are this mild, summer heat limits the garden as much as frost does, and most planting happens in fall and late winter. Your county's extension office publishes a calendar made for your climate.
| When | What to do | Why then |
|---|---|---|
| January | ||
| January 9 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| January 23 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| January 23 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| August | ||
| August 4 to 18 | Cabbage for fall Start seeds | set the plants out by September 22 |
| August 24 to September 7 | Broccoli for fall Start seeds | set the plants out by October 12 |
| October | ||
| October 3 | Snap beans for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| October 7 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| October 8 | Cucumbers for fall Last date to sow | 55 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| October 12 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| October 13 | Summer squash for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| October 17 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| October 24 to November 21 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| October 27 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| November | ||
| November 6 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| November 7 to December 5 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| November 16 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| November 21 to December 12 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| November 28 to December 12 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| December | ||
| December 5 to 19 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| December 5 | Tomatoes, peppers, squash, melons, cucumbers Watch the forecast from | in 1 fall in 10 the first frost comes by this date; pick tender crops before a frost |
| December 12 to 26 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| December 12 to 26 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| December 26 to January 9 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| December 26 to January 9 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
Want more insurance? Shift every spring date 43 days later. That plans around February 21, the date after which only 1 spring in 10 has a frost.
For spring bulbs such as tulips and daffodils, plant once the soil has cooled to about 50 to 55°F and keep going until a couple of weeks before the ground freezes. Our guide to fall planting explains how to tell.
Where these numbers come from
These dates come from NOAA's weather station Riverside Municipal Airport (station USW00003171), 3 miles from the center of Riverside. It sits at about the same elevation, 800 feet above sea level. NOAA rates this station's record as representative: at least 10 of the 30 years, with the gaps filled from nearby stations.
The same station also gives the frost dates for Corona, Jurupa Valley, Colton and Rancho Santa Margarita.
Our ZIP code lookup matches these 5 ZIP codes to the same station, so they get the same dates: 92505, 92879, 92881, 92882, 92883. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Fontana, California: frost not every year (15 miles away)
- San Bernardino, California: frost not every year (15 miles away)
- Menifee, California: frost not every year (20 miles away)
See frost dates across California, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.