Activity for Kristen

I am getting married on the beach and was wondering what I should put on the invitation for attire. I don’t want anyone wearing shorts. Should I say semi-formal?

I am getting married June 3, 2023. When would be a good time to send out the invitations? Most of our guests are coming from out of town, so I want them to have plenty of time to either get a hotel room and/or flights.