Cobb County Master Gardeners Lunch and Learn: Hydrangeas, the Garden Favorite. Master Gardener Debra Stockton will discuss hydrangeas from A to Z, including P for pruning, and heirloom favorites as well as the trendy new cultivars. Free. Bring your lunch. 12-1pm. Cobb County Water Lab, 662 S. Cobb Drive, Marietta. More info: 770-528-4070 or cobbmastergardeners.org.