I think both are correct and would make sense to any English speaker. It depends which English speaking country you are from for what sounds 'natural' though- for example in Australia we would say- 'in summer' or 'in the summertime'. .........In the summer- sounds like an American way of saying it.

In summer

Both are correct. Which one you choose is based on what country or region you are in, or personal preference.

thanks

in the summer