Climate Zones

• The United States Department of Agriculture provides a plant hardiness zone map that divides the continent according to specific climate zones. The map includes 10 separate zones that represent the winter hardiness of plants grown within these locations. Zones with lower numbers indicate shorter growing seasons. Plants grown in colder zones usually require later planting in the spring than those grown in warmer climate zones.
  
  

Plant Types

• Many annuals -- including the majority of garden vegetables and numerous flowering plants, such as tomatoes, peppers, rosemary and cosmos -- are cold-sensitive, meaning they require warm soil temperatures to germinate. Planting these varieties before the final frost in spring can result in plant loss due to freezing temperatures. Plants that require longer growing seasons are suitable for starting indoors in cooler climates. In climate zones 9 and 10, planting is suitable during most months of the year. Many root crops withstand colder temperatures, making early spring and late fall the best times to plant them in the garden.
  
  

Indoor Planting

• Planting seeds indoors about four to six weeks before the final frost in spring helps give them a head start, a necessary practice in climate zones colder than zone 6 or 7, depending on the variety of plant. For instance, long-season tomatoes, such as better boy, require as many as 75 days to mature and begin producing fruit. Starting these early provides a longer season for harvesting fresh tomatoes. Perennial flowers that bloom the first year often benefit from indoor planting, while flowering plants that don't start blooming until the second year make good specimens for planting directly outdoors after the nighttime temperatures remain above freezing.
  
  

Late Season Planting

• The best time to plant spring-flowering bulbs is in the late summer and fall. Planting during this time gives the plants adequate time to begin forming roots prior to freezing temperatures. Early fall is also the best time to divide the plants that supply the new bulbs, tubers and roots. The best time to plant most varieties of shrubs and trees is during the fall season, at least six to eight weeks before the first winter frost. This allows several weeks for establishment before the plants go dormant for the winter. While spring planting can shock a plant and set back the growth for the current year, planting the previous fall helps them get off to a good start when the spring moisture arrives and the sun begins to warm the soil.