Tuesday, January 19, 2010

Average Frost Dates for Selected California Locations

For the longest time, 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 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. You may have noticed, that as a delayed result of the December freeze in Northern California, many plants that looked OK immediately following that cold blast are looking rather sad right now.

But put away those pruning shears.

Take a close look at that suffering geranium, alstroemeria and hydrangea.

New buds and shoots are starting to pop out. Leave that dead foliage on until the danger of frost has mostly passed. Also, don't give up (or dig out) those plants that look bad but haven't produced any new growth yet. Some plants take their sweet time to send out new shoots, possibly as late as mid-spring.


For the weather geeks among you, here are more average frost dates in California.

Average Frost Season (50% Probability) for Selected California Locations
(source: National Climactic Data Center. Includes data for all states. Large file.)

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 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 comment:

  1. great basic post. I pruned some shrubs in December ... plumbago, geranium, lantana (prob. ok) ... feeling guilty as I snipped. Now you confirm what I thought the whole time...don't cut it, leave it on ...but, it looked so much better. Hope there's life still there!