Determine Your Zone

• Learn which hardiness zone you reside in, and then choose a dahlia breed suitable to your region. The zones are determined by lateral location and not the state or province individually. For instance, upper Florida is in the 8b zone, while the tip of southern Florida is 10a. There are four zones in Florida, depending on average temperature in the winter and the spring/summer growing season.
  
  Parts of the western United States vary widely because of sea level variations. Las Vegas is in the 9a zone while Salt Lake City, Utah is in 6b. Great Falls, Montana sits in the 3b zone and zone 4b crosses over Sioux City, Iowa. When determining your zone, use a zone map as a reference to your planting. This map is valid for all fruits, vegetables, and flowering plants.
  
  

Choose the Right Dahlia for Your Zone

• Read the information listed beside the dahlia you wish to purchase. Seed packets and informative cards sold with potted plants all have a zone map and listing for the particular zone the plant grows best in. If you purchase a dahlia set for zones 8 to 10, and you live within a 6, the dahlia will grow weak and lose color because it is not suited for cold weather. In addition, some dahlias state that they can survive well in a zone 4, even though they are recommended for 8 to 10.
  
  The akita and the bishop of oxford dahlias are hardy in zones 8 to 10, but still fine in zone 4. The Mr. Optimist and Thomas Edison dahlias are hardy in zones 8 to 10 but can also grow in zone 3. All dahlias are best suited for zones 8, 9, and 10. They may also do well in a cooler climate, such as zones 3 and 4, particularly because they can grow dormant and return the following spring to bloom.
  
  

Dahlias for Ill-Advised Zones

• If you live within zones 5 and 6, from northern Texas, Oklahoma and through central Illinois, your dahlias may not be as lush and prosperous as they would in their recommended zones. Likewise in zones 1 and 2, toward northern Canada.
  
  Living in these areas does not mean you cannot have dahlias. You will not have healthy dahlias by planting them in cold ground, though you may have them in containers. Keeping your dahlias inside over the winter and away from extreme wind and heavy rainfall will ensure they will thrive in any zone.