What zone are you in?

Garden zones are a way of labeling areas that share common climate traits.  There is the USDA Plant Hardiness Zone Map and then there is the Sunset Zone Map. Let's take a look at both and what they can tell us.

USDA PLANT HARDINESS MAP

The  USDA Plant Hardiness Zone Map defines zones according to plant hardiness and is based on the average annual minimum winter temperature.  In Corona, Ca. where I live, we are zone 9b, with an average low temp of 29 degrees.  Plants can freeze in many neighborhoods in Corona. This is one of the first garden lessons many folks learn when they move here from Orange county. It is colder here. And the USDA zone assignment can tell you that.

We are not only colder in the winter,  we are hotter in the summer and over all we are drier than Orange county.  The foothills that I love to the south and the west of my home also block any chance of a cooling ocean breeze. 

Sunset Garden Zones are much more definitive than the USDA map and take other factors into consideration along with average low temperature. Here is an example of the difference that can make:

• El Centro. One of the hottest and driest cities in So Cal is assigned to USDA zone 10a.
  • El Centro is inland and has an average high temperature in July of 107 degrees, with an average annual rainfall of only 3 inches for the entire year. 
• Oceanside on the Pacific coast is also assigned to USDA zone 10a.
  • Oceanside is located on the coast and has an average high of 70 degrees in July with an average annual rainfall of 10.3 inches.

Expecting plants to perform equally well in either location because they both are assigned the USDA 10a zone is asking for trouble.  There is no comparison, and this is why knowing your Sunset Zone is going to be most helpful when it comes to your garden. In the map below you can see Corona, where our beloved 91 fwy and the 15 fwy meet. Our zones are 18 or 19.   

Sunset publications have been an excellent resource for gardeners in the western united sates for over 100 years. The Sunset Western Garden Encyclopedia is considered the 'bible' of the garden industry.  If you don't have a copy yet, pick one up.