Friday, November 5, 2010

Frosty News for the Worried Gardener

For the longest time (including last week in this space), I have been telling anyone who would listen that the average frost season for Sacramento (the first and last dates of the garden year when temperatures may dip below 32 degrees) is Dec. 12 through January 27.  

The record dates for earliest and latest frosts for Sacramento, however, stretch even longer: Nov. 4, 1935 and March 27, 1898. (source: National Weather Service Office, Sacramento.)
Like many statistics, those average frost dates are written in sand, depending on who you talk to (and, of course, location).

The dates for the "frost season" are important to gardeners for many reasons, especially to determine when to gear up to protect those plants that may be damaged by the cold, especially citrus fruit and containerized subtropical plants that may need to get moved to a warmer location.
Another consideration: those frost season dates can help you ascertain how long to leave freeze damaged (or dead) branches on bulbs, perennials and shrubs. By leaving on those dead portions, the understory of the plant is given some protection to produce new shoots, especially near the base of the plant.

But are "average" frost dates good guidelines for the backyard gardener?

The National Climactic Data Center prefers to define "average frost dates" as those which include a 50% probability of frost, stretching out the chances of your "frost season" by several weeks.
For the gardener who worries about everything (as well as the weather geeks among you) here is a more realistic frost date chart for California:

Frost Season (50% Probability) for Selected California Locations

Bakersfield: Dec. 11-Jan. 31
Chico: Nov. 15-Mar. 20
Davis: Nov. 24-Mar. 4
Eureka: Dec. 15-Jan. 30
Fresno: Nov 25-Feb. 22
Lakeport: Nov. 2-Apr. 20
Livermore: Nov. 13-Mar. 29
Lodi: Nov. 16-Mar. 6
Los Angeles: rare
Marysville: Dec. 2-Feb. 9
Modesto: Nov. 29-Feb. 21
Napa: Nov. 26-Mar. 20
Nevada City: Oct. 15-May 17
Placerville: Nov. 6-Apr. 25
Sacramento: Dec 1-Feb. 14
San Francisco: Jan. 5-Jan. 8
San Jose: Dec 25-Jan. 22
Santa Rosa: Nov. 19-Mar. 25
Sonora: Nov. 12-Apr. 14
Stockton:Nov. 22-Mar. 1
Truckee: Aug. 16-July 11
Ukiah: Nov. 10-Apr. 3
Vacaville: Nov. 18-Mar. 19
Willows: Nov. 23-Mar. 14
Winters: Nov. 27-Feb. 17
Woodland: Nov. 26-Feb. 28

But, wait. What if you are the gardener who truly takes that seed packet statement, "Plant after all danger of frost" very seriously? What if a 50-50 chance of temperatures falling to 32 degrees or lower is too risky for you?  

Then heed this list of possible frost dates, which extends the frost calendar to include as little as a 10% chance of frost:

Bakersfield: Nov. 20-Mar. 3
Chico: Oct. 30-Apr. 23
Eureka: Nov. 15-Mar. 14
Fresno: Nov. 7-Apr. 1
Lakeport: Oct. 10-May 10
Livermore: Nov. 3-Apr. 27
Lodi: Nov. 2-Mar. 31
Los Angeles: Jan. 2-Jan. 3
Marysville: Nov. 14-Mar. 16
Modesto: Nov. 10-Mar. 20
Napa: Nov. 9-Apr. 20
Nevada City: Sept. 24-June 4
Placerville: Oct. 22-May 18
Sacramento: Nov. 14-Mar. 23
San Francisco: Dec. 1-Feb. 9
San Jose: Nov. 23-Feb. 19
Santa Rosa: Nov. 5-May 1
Sonora: Oct. 26-May 10
Stockton: Nov. 5-Mar. 30
Truckee: July 31-July 27
Ukiah: Oct. 25-Apr. 29
Vacaville: Nov. 4-Apr. 24
Willows: Nov. 8-Apr. 23
Winters: Nov. 13-Mar. 27
Woodland: Nov. 5-Apr. 1


  1. Love that range in Los Angeles, Jan 2-3!!! It was fabulous to garden in coastal So Cal. Gardening in eastern Sac county it is a different animal entirely.
    We had frost here a week ago - it October!

  2. This is great, Fred! Frost is a big deal for our area, and it's important to understand how to protect vulnerable plants. I usually use the bring potted plants close to the house, and last year I purchased some professional grade frost (blanket) protection from Windmill. I figure I was safe to around 25 degrees.

  3. A little frost brings out the ZING in citrus -- and can also be good for stonefruit trees -- but I really hope that we can avoid the deep freeze that hit last December. The lime tree really took off this summer in terms of new growth -- but that new growth is also susceptible to frost damage (as I was chagrined to discover last year).