Polite way to say dress up!

I'm planning my daughter's wedding, it will be outdoors under a pavilion on someone's property (they rent it out for weddings), even though the cost of it is similar to having it at any high end place around here (my daughter wanted space and outdoors and fell in love with the place and the owner, it is beautiful!). So the reception will be a formal dinner, but "outside". I'm afraid people will think they don't have to dress up though. Can I say "formal reception to follow" and they'll get it? I don't want how people dress to cheapen her wedding. And heck I would do it casual if people will dress casual. But maybe that's the chance we take having it outdoors, OR should I just do the reception more casual anyways?