At the end of most plant listings you'll find zone numbers, e.g., Zone 8. These refer to U.S. Department of Agriculture plant hardiness zones. They are determined by your range of annual average minimum temperature. For example, if your coldest winter temperatures are between 10 and 20 degrees F, you live in zone 8. If your temperatures are as low as -20 to -10, you're in zone 5. If you live in zone 5 and you buy a plant rated at zone 8 and plant it outside for the winter, it will most likely die, because it can't take winters as cold as yours.

These zone designations only consider temperature, but other factors can enter into hardiness. For example, Zone 8 in the Pacific Northwest has very rainy winters that will rot some plants that will grow well in zone 8 in Texas. Other plants may do well in the dry northwest summers, but not so well in the humid summers of the south.

Remember that hardiness zones apply to plants in the ground. Plants in pots are more likey to freeze, even if they are rated for your zone. Also, just because your climate is warm doesn't mean you can grow anything. Some plants that are adapted to cold climates need cold winters.

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