Answer: The reference I rely upon most is Sunset Western Garden Book. The authors have gone one step beyond the standard USDA climate zones by considering elevation and proximity to bodies of water and then assigning zone numbers. According to them, you're in zone 5 with average winter lows in the mid 30's and a 225 day growing season.
This zone correlates most closely to USDA zone 9 but the summer temperatures will be a bit lower in Florence and you'll have a bit more cloud cover during the summer months. This cooler summer weather will affect the ripening of long-season veggies such as tomatoes and squash and you may want to avoid heat-loving perennials such Lantana and Ice Plant.
If you're a vegetable gardener, a good source of seeds for planting in short, cool-summer regions is Territorial Seed Company (visit their website and request a current catalog).
Roses and most other sun-loving perennials should be placed in your garden where they will receive maximum sunshine during the summer months (8 hours of direct sunshine will keep your rose bushes happy and healthy).
Since you're new to the area you might want to explore local parks and take note of the plants growing there. Most city landscapes include perennial plants hardy to the area. Be sure to stop by the library for a copy of Sunset Western Garden Book!
Best wishes with your new landscape!
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