According to PlantMaps.com, the average last frost date for Redding, California, is anywhere between March 1 and March 31, depending on your exact location. Go to http://www.plantmaps.com/index.php to find a ton of helpful gardening information for the US.

Below is actual weather data for my area, taken from two different sources. Both sources happen to be in the same zone 9a, according to the USDA Hardiness Scale, which has the average last frost between March 11 and March 20. Keep in mind that the “average last frost date” means that there is a 50% chance that the last frost will actually occur AFTER this date, in other words, it’s potentially only 50% right. As you can see from 2011 and 2013 data, our actual last frost was 6 and 2 days after the predicted March 20th.

	2007	2008	2009	2010	2011	2012	2013	2014
Last Hard Frost	—	Feb 4	Feb 10	Mar 10	Feb 27	Mar 2	Mar 22
Last Soft Frost	Mar 1	Apr 24	Apr 15	Apr 6	Mar 28	Apr 4	Mar 8
Spring Lows < 45ºF	Apr: 10  May: missing data	Apr: 20 May: none	Apr:15 May: none	Apr:17 May: 7	Apr:16 May: 12 Jun: 2	Apr: 17 May: 1 Jun:2	Apr:?

Hard Frost: more than a few degrees under freezing (32 deg), for more than a few hours

Soft Frost: just barely under freezing