Riverside, CA Frost Dates: Last Spring and First Fall Frost

In a typical year the final freeze of spring reaches Riverside around January 9, and the first freeze of autumn returns around December 25. NOAA's normals call the frost-free stretch between them 353 days long.

Because half of all years do worse than the typical date, the dates that matter for tender plants are the late spring date, February 25, and the early fall date, December 1, each of which one year in ten fails to beat. Riverside's season is 124 days longer than the 229 days median across the 100 cities on these pages, which puts it 4th for season length.

These dates come from the NOAA weather station Riverside Fire Station 3 (ID USC00047470), 0.9 miles north of the Census Bureau's internal point for Riverside, at about 840 feet above sea level.

When is the last frost in Riverside?

One year in ten has a freeze on or after February 25. In nine years out of ten there is still a freeze on or after December 16, and half of years see one on or after January 9.

There are 71 days between the early and late dates, a broader band than most cities on these pages show. In Riverside the typical date is a weaker promise than it looks.

When is the first frost in Riverside?

NOAA's early fall date for Riverside is December 1, its even-odds date is December 25 and its late date is January 27; the first freeze has come by each of them in one, five and nine years out of ten.

From the 10% date to the 90% date is 57 days, a wide band here, and the early date arrives 24 days before the typical one.

The growing season in Riverside

With a season well beyond the middle of these pages, Riverside has days to spare for slow crops, as the planting dates below show. Season length swings more here than in most of the 100 cities: 353 days in a typical year, 307 days in a short one, a difference of 46 days.

NOAA counts these days from its own simulations, so they will not equal the number of days between the two typical dates exactly. Frost is not guaranteed: 68.8% of years reach 32°F at Riverside Fire Station 3, and the other 31.2% never do, so read the dates as when a frost can happen, not as an appointment.

28°F dates in Riverside

A hard freeze follows the first frost quickly in Riverside: the typical 28°F night arrives on December 29 in fall, only 4 days after the first 32°F one on December 25, and in spring the last one comes on December 31, 9 days before the last 32°F frost. Tender plants get little warning here. The late 28°F spring date, January 16, is the one that still catches blooms and young transplants one year in ten, and the early fall date, November 30, is when a hard freeze has arrived in one fall out of ten.

What this means for planting in Riverside

The University of New Hampshire Extension sheet times each crop from the last frost. For Riverside's typical date, January 9, that means cabbage on December 12, lettuce from December 12 to December 19, seed potatoes from December 26 to January 2, and, once the frost is behind you, peppers on January 23 and beans on or after January 9. Peas have no frost-based date in the University of New Hampshire Extension sheet: they go in as soon as the soil thaws.

47 days lie between the typical and late dates in Riverside, enough to decide whether you plant tender crops early with a cover ready or wait for a safer spring.

For fall, NC State Extension gives each crop's days to harvest, and University of Georgia Extension adds a harvest allowance of 18 days; you count back that total from the first frost. Every one of the 34 fall crops in the fall planner still has a last planting day on or after July in Riverside. Of the crops that fit, parsnips is the slowest: 148 days from planting to the early frost, which makes July 6 its last day.

Worked example: planting broccoli for fall in Riverside

Work through broccoli transplants for fall in Riverside. The longest days to harvest NC State Extension gives is 80 days, plus University of Georgia Extension's allowance of 18 days, for 98 days in all. Subtract that from the typical first frost on December 25 and the last day to plant is September 18; subtract it from the early date on December 1 and it is August 25.

24 days separate the two last days, enough that in Riverside the earlier one is worth following.

The same crop family has a spring clock too. University of New Hampshire Extension sets cabbage out ahead of the last frost, and from January 9 in Riverside that means on December 12.

Where Riverside's numbers are measured

The station is 0.9 miles north of the Census Bureau's internal point for Riverside, close enough that its record is the natural reference for the city.

Its elevation is about 840 feet. Of the 100 stations behind these pages, 35 sit higher and 63 lower. NOAA flags this station's record as representative, the code R, for the data behind its 50% last-frost value.

Because the Census file has no elevation for Riverside, we cannot say how far your yard is above or below this station. When yours is clearly higher or lower, open the nearby stations in the frost dates tool and favor the colder one.

How Riverside's frost dates compare

San Bernardino, CA is only 15 miles away and shares the region, while the other two cities below are farther out and show how the dates change with distance. Note that the San Bernardino station stands 560 feet higher than Riverside's.

• San Bernardino, CA (15 miles, north): spring frost lingers 18 days longer than in Riverside, and the season runs 24 days shorter. Its typical dates are January 27 and December 19, with 329 days frost-free.
• Bakersfield, CA (135 miles, north-west): spring frost lingers 22 days longer than in Riverside, and the frost-free season is 41 days shorter than Riverside's. Its typical dates are January 31 and December 8, with 312 days frost-free.
• Henderson, NV (196 miles, north-east): the last frost is 11 days later than in Riverside, and the frost-free season is 20 days shorter than Riverside's. Its typical dates are January 20 and December 15, with 333 days frost-free.

Put the frost dates to work

The frost dates tool opens on this station and lists every probability date, not just the ones above. From there, the spring planting planner and fall planting planner turn the dates into crop lists for Riverside, and the hardiness zone lookup answers what will overwinter.

Every city covered is on the city frost dates index, sorted by state.

For California, the state planting pages copy the Extension calendar (UC Master Gardener Program) crop by crop and region by region: tomatoes in California, peppers in California, cucumbers in California, summer squash in California, green beans in California. Set those windows beside the frost dates above.

Where these numbers come from

Every frost and freeze date comes from the station's entry in NOAA's U.S. Climate Normals for 1991–2020 (doi:10.25921/4ek7-fk11), with no adjustment, and NOAA's documentation explains what each probability means. Riverside and its internal point are listed in the Census Bureau's 2024 Gazetteer of places; its place in the ranking comes from the Vintage 2024 population estimates, which count 323,757 residents.

The planting dates apply the count rules in University of New Hampshire Extension, NC State Extension and University of Georgia Extension to this station's dates, with nothing added. The methodology page explains how each figure is checked.

NOAA's dates say how often frost has come, not when it will. Check the forecast before planting and keep a cover on hand.