I was hoping more people would post as I'm not experienced but if your petunias became leggy I,m wondering why .
Perhaps others can say but maybe not enough light ? Or something about the compost they are in ,too rich ? I've googled leggy plants and don't quite understand it ,soory 
I plant pots and use geraniums both the ivy leaf trailing ones and the upright ones ( they like it on the dry side ) and lobellia .
This below is from Alan Titmarsh
Use a peat-free, multipurpose or potting compost, roughly half-filling your container and mixing in some slow-release feed granules. You could also add some water-retaining granules.
Reconstitute these into a thick paste, then stir into the compost to assist moisture retention in hot, dry weather. This is particularly helpful for hanging baskets
Don’t economise on plants – buy enough to fill each container completely,.
remove the pots by upturning each plant and gently tapping the rim of its pot on a hard surface so the root ball slides out into your hand. Stand the root balls in place, so they’re touching, and turn plants round so their best side faces outwards.
Fill the gaps between plants with more compost, then spread a little more over the surface of the root balls so they are buried (but only just). When you’ve finished, the surface of the compost should be about an inch below the rim of the container, to allow room for watering.
the surface of the compost should be about an inch below the rim of the container, to allow room for watering I've often not managed to achieve this ,what with cramming plants in as recommended but it's really important as otherwise the water just runs off when you water .
Then water well to settle the compost round the roots
Care
Every day
Check to see if containers need watering; do the “finger test” and water if the compost starts to feel dry. Newly planted containers won’t need a lot of watering but by early July, they will be full of roots so anticipate extra watering. The height of summer hot weather often means containers need watering once or even twice a day.
Every week
Pick containers over, remove dead flowers and dead or yellow leaves.
Feed once a week with liquid tomato feed, diluted to half the usual strength, from July onwards. A packed tub will be ready for a top-up by then. If you didn’t use slow-release feed, you’ll need to liquid feed at every other watering, from mid June.