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.