According to your zip code you are in zone 8A. Zone maps are based on the average minimum winter temperature, and winters are seldom average! No matter where you live in the U.S., if you are near the border between zones, you will find that plants for the zone below you may suffer damage in your site in winters a bit colder than average. Plants designated for the zone above you, but not below you may suffer too much in the sultry heat of summer. I suggest that as a rule of thumb you select plants listed as being adapted to the zone above you. Also include a few favorites from the zone below you, which you do not mind protecting during an unusually cold winter period.
That said, cold hardiness is most meaningful in the low end of the range, that is how cold of a zone a plant can take. The high end is not necessarily that relevant but does give a general guide as to how far south a plant may be adapted. The southern range of a plant is better determined by looking at the heat zone rating. The high end of the heat zone rating is your cue to whether a plant can take your area's summer heat.
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