Zeroing in on Zones

A woman recently moved to Santa Fe from San Diego and wrote in asking if zones really mattered. "I've never paid any attention to them. Should I? Do I have to?" she wondered.

  • Topic: Plant Selection
  • Author: High Country Gardens
  • Keywords: zones, degrees, fhrenheit, USDA,
  • Date: February 2006

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A woman recently moved to Santa Fe from San Diego and wrote in asking if zones really mattered. “I’ve never paid any attention to them. Should I? Do I have to?” she wondered.

I’ve had this conversation before with new arrivals; my standard reply is: “If I didn’t, I wouldn’t have a garden.” Then again, tending to zone designation doesn’t guarantee success in the garden. There are lots of other considerations. I didn’t want to diffuse her enthusiasm too quickly, though.

“I see plants in your catalog marked Zones 4 to 9. What exactly does that mean?” she wanted to know.

It’s simple: if temperatures are too cold for a plant, that plant won’t make it through the winter. The plants have to be equipped to produce the correct chemical processes needed to ensure winter cold-hardiness.

Santa Fe’s zone is 5; or 4 and 6, depending on where plants are placed, along a south facing wall, in the shade on the northern side of the house or out in the open. It can get tricky.

Below is a basic hardiness zone chart with degrees in Fahrenheit. The zones refer to minimal air temperatures reached during the winter.

Zone Temperature Note
1 Below -50°
2 -50° to -40°
3 -40° to -30°
4 -30° to -20° soil freezes solidly and deeply from late fall through early spring
5 -20° to -10° soil freezes more deeply for the winter
6 -10° to 0° soil will only freeze down to 1 to 3 inches for a few weeks at a time
7 0° to 10° soil rarely freezes more than just below the surface
8 10° to 20°
9 20° to 30°
10 30° to 40°
11 above 40°

If a freak cold snap hits one night in a warm climate, it doesn’t mean all the plants will die. Low temperatures may cause cellular damage, but it may not be fatal if the low temperatures only last a day or two. Still considering zones is a good idea if you want to save most of your garden.