Hello, winston1425. Drooping is normal during the summer and new hydrangeas tend to recover on their own by the time the sun goes down. As the years pass, they get used to that and droop less. If the event looks extreme, water them 1 gallon of water immediately. Otherwise test the soil with a finger and water only if the soil feels almost dry or dry.

As far as what fertilizers to use, you can use cottonseed meal, compost or composted manure. If you like to use chemical fertilizer, choos a general-purpose slow-release fertilizer with a NPK Ratio like 10-10-10. Make sure that all the extra watering that they need when potted does not cause the soil to be defficient in phosphate. They also need a few hours of sun. Dappled sun is fine.

Luis