The National Gardening Association website has a wealth of resources for managing a garden. Including regional reports:
For the middle-south, “With year’s hottest and driest weather just ahead, it is best to delay the planting of tress and shrubs until autumn, when the odds of successful establishment are more favorable.” – St. Claire, 2010
They also have some nice how-to videos and instructional pages on topics like planting tomatoes and starting vegetable seeds (for the plant sale).