Plants and winter cold
Successful landscaping depends upon a choice of plants that thrive on the land they adorn. Since soil conditions and moisture levels can usually be altered artificially, limitations on where plants will flourish depend largely upon the severity of winter cold. This map devised by the U.S. Department of Agriculture divides the United States into 11 numbered and colored zones, each distinguished by an average minimum winter temperature. Use the charts of ground covers (pages 267-269), flowering shrubs (pages 275-278), and rock-garden plants (page 280) with this map to select plants that will grow best in your area.