Which frost date do the crop weeks use?

Weeks after the frost-free date use the median last 32°F date, January 17, when the guide does not name a probability. Weeks before the first freeze use the median first 32°F date, December 19. Both medians are 50% dates in the NOAA 1991–2020 normals for the station on this page. The page says when that anchor was used.

Where do the crop dates come from?

Crop dates come from the extension guide cited on this page, not from a second calendar invented here. The publisher and the title are printed with the source note. A month without a day is expanded to the first and last day of that month, and the page says so. A phrase without two dates stays a phrase.

Is this planting calendar a forecast?

No. The frost dates are 1991–2020 climate normals at the station 5.6 miles from the city point. The crop windows are the cited guide’s ranges, shifted only when that guide itself used weeks. A cold spring can still fall past the median. The National Weather Service forecast covers a particular night. This page does not.

Planting calendar for Chino Hills, CA

Direct answer. In Chino Hills, CA, the median last 32°F date at CHINO AP, CA US (USW00003179) is January 17, and the median first 32°F date is December 19. The station is 5.6 miles from the city point. Crop windows come from UC ANR, UC Master Gardener Program. Where that guide counts weeks from a frost date and does not name a 10%, 50%, or 90% level, those weeks are applied to these median dates.

Median last 32°F January 17. Median first 32°F December 19. Frost dates for Chino Hills.

A wall calendar surrounded by vegetables, herbs, seed packets, and watering cans.

Median last 32°F is January 17. Median first 32°F is December 19. The 50% growing-season length is 335 days. The green band runs from the median last frost to the median first frost. Thin ticks mark the 10%, 50%, and 90% dates.

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Last 32°F in spring

NCEI’s probability is the chance the last spring minimum of 32°F or lower occurs on or after the date.

Probability	Date	How to read it
90%	December 18	Earlier date. A last 32°F on or after this day is common.
50%	January 17	Median.
10%	February 22	Later date. A last 32°F on or after this day is uncommon.

First 32°F in fall

NCEI’s probability is the chance the first autumn minimum of 32°F or lower occurs on or before the date.

Probability	Date	How to read it
10%	November 27	Earlier date. A first 32°F on or before this day is uncommon.
50%	December 19	Median.
90%	January 17	Later date. A first 32°F on or before this day is common.

32°F growing-season length

Days between the last spring 32°F and the first autumn 32°F. The figure is a length the season meets or exceeds at that probability, from NCEI, not a subtraction done on this site.

Probability the season is at least this long	Days
10%	365
50%	335
90%	293

28°F threshold

	10%	50%	90%
Last, on or after	January 28	January 3	December 11
First, on or before	December 7	December 30	January 23
Season at least	365 days	365 days	346 days

36°F threshold

	10%	50%	90%
Last, on or after	March 29	February 24	January 21
First, on or before	November 12	December 1	December 18
Season at least	316 days	278 days	241 days

Station CHINO AP, CA US (USW00003179). Completeness flag R, 18 years used for the 32°F dates. NCEI’s annual probability of at least one day at or below 32°F is 85.4%. Freeze dates are conditional on that threshold occurring. Elevation 198.1 m. The same probability language applies to the 28°F and 36°F rows when those dates passed the same quality checks.

Questions

Which frost date do the crop weeks use?: Weeks after the frost-free date use the median last 32°F date, January 17, when the guide does not name a probability. Weeks before the first freeze use the median first 32°F date, December 19. Both medians are 50% dates in the NOAA 1991–2020 normals for the station on this page. The page says when that anchor was used.
Where do the crop dates come from?: Crop dates come from the extension guide cited on this page, not from a second calendar invented here. The publisher and the title are printed with the source note. A month without a day is expanded to the first and last day of that month, and the page says so. A phrase without two dates stays a phrase.
Is this planting calendar a forecast?: No. The frost dates are 1991–2020 climate normals at the station 5.6 miles from the city point. The crop windows are the cited guide’s ranges, shifted only when that guide itself used weeks. A cold spring can still fall past the median. The National Weather Service forecast covers a particular night. This page does not.

Crops in the cited guide

Chino Hills, CA

Zone 10aAverage annual extreme minimum 30°F to 35°F

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

California. Nearest qualified station: CHINO AP, CA US (USW00003179), 5.6 miles. Median last 32°F January 17. Median first 32°F December 19. The 50% growing-season length is 335 days.

Open the ZIP page · Crop guides for California

32°F probabilities at this station

	10%	50%	90%
Last 32°F on or after	February 22	January 17	December 18
First 32°F on or before	November 27	December 19	January 17

Column order matches the NCEI file: for the last freeze, 10% is the later date and 90% is the earlier date. How to read the probabilities.

Planting calendar

Windows below are from UC ANR, UC Master Gardener Program, Time of planting, retrieved 2026-10-10. North and North Coast = Monterey County north; South Coast = San Luis Obispo County south; Interior Valleys = Sacramento, San Joaquin, and similar valleys; Desert Valleys = Imperial and Coachella Valleys. Source line on the page: California Master Gardener Handbook, Table 13.2, Adapted from Vegetable Gardening Illustrated 1994.

Crop

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State crop pages: Beans, snap · Beets · Broccoli · Cabbage · Carrots · Corn, sweet · Cucumbers · Eggplant