Water.....every day and twice when it's hot dry and windy....The amount of rain that falls into a hanging basket is very very small. You need to water until water runs out the bottom and then do it again. Once you get the soil in the pot thoroughly wet, water that pot every day at least once until water runs out the bottom. If a pot dries out it can be hard to re wet the soil, the water runs out without wetting the root ball.
And don't ever ever put any fertilizer on a plant that is dry.
It will taks several weeks for that plant to get looking good. After a couple of seeks, cut back anything that looks ratty and keep watering!
Once the plant has started to put out some new growth, you can put on 1/4th strength a mirical grow solution.
Good luck.
Linda C

Don't water your plants everyday if they don't need it, too much water can be just as bad as not enough. When I water my pots and containers, I stick my finger in about 1" deep at the base of the container, if it feels wet/damp, then don't water, if it's somewhat dry, then water. Petunias do not like to be waterlogged nor do they like to dry out.

If your weather is scorching hot like ours right now you will have to faithfully check its watering needs everyday, maybe twice a day.

For pots and containers, fertilize with Miracle Gro 15-30-15 once a week, deadhead and cut back every other stem every now and then to keep them compact and bushy.

Sharon