Know Your Zone

• Because temperatures vary so widely among different regions of the country, the United States Department of Agriculture (USDA) divided the nation into numbered zones. Find out which zone you live in to learn when it is typically safe to plant outdoors. Then you can determine the date on which you should start flower seeds in a greenhouse. United States zone maps are viewable online at a variety of websites, including www.e-bloomin.com.
  
  

Plan for About Eight Weeks of Greenhouse Growing

• Start most of your flower seeds in the greenhouse about eight weeks in advance of the anticipated date of the last frost in your zone. For example, if you live in Zone 4, you know that the last frost of your winter season typically occurs at the end of May. Consequently, start a majority, if not all, of your seeds at the end of March, eight weeks before then.
  
  

Read Your Individual Flower Seed Packets

• Because different flower seeds have varying needs, the instructions on some flower seed packets may suggest starting certain seeds more or less than eight weeks before the last frost. For example, geraniums and licorice plants need 12 weeks to grow before they can be transplanted outdoors. Impatiens, lobelia and petunias need between 10 and 12 weeks. And morning glories require only six weeks. Nasturtiums, cosmos and zinnias can often be sown directly outside, but if you want to start these stronger flowers in a greenhouse, do so six weeks before the last frost.