The Q&A Archives: USDA Zones

Question: We live at 7,200 ft. in the San Bernardino Mountains in So. Ca. Sometimes (not often) in the winter it gets down to -10 degrees, but usually the temps are 15-20 degrees. It is also quite dry. What zone are we, and what is the difference between the USDA zone and local zones?

Answer: USDA Zones are a general guideline based upon average winter lows and first and last frost dates for a large, general area of the country. Each garden is unique in that there are factors that create micro-climates, both within the landscape and from the surrounding area. These factors can include elevation, mountains, hills, bodies of water, buildings, stands of native trees, open meadows, prevailing winds, etc. A better guide for you would be the zone identified in Sunset Western Garden Book. The authors have gone to great lengths to reclassify general zones, breaking them into sub-zones, based upon local influences. You're in Sunset's zone 2, the second coldest western climate. You can expect snow in the winter, along with cold air. Your growing season is mid-May through mid-September. For a more detailed description, plus suggestions for plants suited to your gardening zone, consult a copy of Sunset Western Garden book, ISBN #0-376-03851-9.

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