I’ve been getting calls and emails about whether it’s time to plant vegetable gardens and summer annuals. The answer is – not quite!   
Atlanta’s last frost date is about April 15th. Some areas outside the city have their last frost up to two weeks later. But frost isn’t the only thing that makes a difference. Most of our summer vegetables and flowers are tropicals. Tropical plants will sit and sulk until the soil is warm enough.
For tropical annuals such as Impatiens, Vinca (Madagascar Periwinkle), Tomatoes, Peppers and Eggplants, wait until the soil is warm. You can check
Georgia Weather Net  for soil temperatures in your area. The soil at root depth should be around 70 for best results.  For best growth of vegetable seeds, this article from the Texas Extension Service is useful.
    One year, I planted tomatoes at one-week intervals starting in early April. The earliest ones died. The rest produced later than those planted in late April. The fastest to produce was that last planted- on May 5th! 

Daryl Pulis,  April 20, 2007  www.Gardens-2-Go.com