Just got an invite for a South Carolina wedding in a garden on August 13th. There's not an indoor backup, so the invite says umbrellas will be provided if it rains.
Forget the rain, which is bad enough, WHY would there not be an indoor backup? What if it's 98 degrees that day? Why would you subject your guests to unbearable heat? There's nothing stopping you from taking photos outside, but why, why, why would you subject your guests to it? That would be like me forcing people to sit in outside for my December wedding because I love the snow.
If the temperature is over 75 degrees or under 60 degrees, your wedding should be inside. If you plan an outdoor wedding without an indoor backup, you're a terrible host.