I'm getting married at a rustic, woodsy Inn venue. Ceremony will be outdoors on grass, reception will be under a tent with a substantial stone floor and dance floor (w/ walls and heaters if necessary). What should I put on my invitation for the dress code? I want people to know that it's not so formal that they can't bring a sweater, and also not to be surprised and get their stilettos stuck in the grass for the ceremony. Should I just put "semi-formal" and trust that adults can dress themselves? Or is there a more creative way to word this properly?