Question
I live in Williamsburg VA (zone 7) and have several flower boxes and hanging baskets of petunias on my upper and lower porches.  They receive full sun but are not blooming as much as I expected.  Have fertilized with Osmocote as instructed and water daily, plants are in open wrought irom frames with coconut lining.  I just don't understand EXACTLY where to cut when deadheading.

Answer
Bette,
To deadhead petunias, cut the thin green stem that is below where the flower formed.  The whole point of deadheading is to cut off the developing seeds that form just under the flower - if the plant hasn't produced seeds, it keeps making flowers attempting to do so.

Petunias will also branch out and flower more if you cut three or four of the stems in half every week -  By this I mean the stems that form the flowers at the ends of their length...if you clip a few in half every seven to ten days, those clipped stems branch out and keep the plant thick and bushy.  Water this plant when the soil is dry - that may be everyday in hot weather, or it might be every three or four days...feel the soil to make sure it's dry before watering.

I hope this helps!
C.L.