Frost dates for Simi Valley, California

Simi Valley doesn't get a freezing night every winter: about 22 years in 100 have one. In those years, half have had their last frost by December 31 and half their first by December 30.

Stations near you disagree. NOAA's Van Nuys Airport (15 miles away, at 770 feet above sea level), the one we used, gives a typical last frost of December 31 and a typical first frost of December 30. NOAA's Woodland Hills Pierce College (10 miles away, at 790 feet above sea level) gives a typical last frost of January 24 and a typical first frost of December 15. So the typical last frost could fall anywhere from December 31 to January 24 and the typical first frost from December 15 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 Simi Valley

Frost risk through the year

JanJFebFMarMAprAMayMJunJJulJAugASepSOctONovNDecD

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.

In a typical year there is no freezing night at all. In 1 year in 10, the longest frost-free stretch is 348 days or shorter.

• Frost possible (36°F at the station): about 82 years in 100 have one. In those years the last typically comes on January 19 and the first on December 22. 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 Simi Valley

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 comes in fewer than half of years here (about 22 years in 100), so we don't build a planting calendar around it: in most years there is no last frost to plant after. Your county's extension office publishes planting dates made for your climate.

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 Van Nuys Airport (station USW00023130), 15 miles from the center of Simi Valley. It sits 120 feet lower, at 770 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 Thousand Oaks, Moorpark, San Fernando and Agoura Hills.

Our ZIP code lookup matches these 5 ZIP codes to the same station, so they get the same dates: 91402, 91403, 91405, 91406, 91411. Hardiness zones are worked out separately for each ZIP code.

Nearby places

• Santa Clarita, California: frost not every year (20 miles away)
• Pasadena, California: frost not every year (35 miles away)
• Torrance, California: frost not every year (40 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.