De or het festivalzomer?

The correct Dutch article is:

de festivalzomer

How to use festivalzomer

the festivalzomerde festivalzomer
this festivalzomerdeze festivalzomer
that festivalzomerdie festivalzomer
our festivalzomeronze festivalzomer
your festivalzomerjouw festivalzomer
every festivalzomerelke festivalzomer
which festivalzomer?welke festivalzomer?
a big festivalzomer / the big festivalzomereen grote festivalzomer, de grote festivalzomer