Majority of concerts are known as "House Concerts" and any concert in the backyard is mostly in the summer months although most concerts I have been to in the summer, are still indoors(majority anyway).
You have to send the person running the house concert information, bio & CD (promotion material). Most house concerts are folk artists who have some degree of a following and established. For example, I have been to in recent years house concerts to see Steve Gillette, Cindy Mangsen, Anne Hills, Priscilla Herdman who are well established folk artists and have a pretty decent following.

If you type in (for example) "House Concerts" in California (or whatever state you will be in) is one way to find house concerts state by state.
Once in awhile you might find someone who is willing to allow a lesser known folk artist open for them at a house concert but that is entirely up to the artist to agree to that as well as the people running the house concert.   

Other then that there are many venues all over the country with "open mike" nights.

Everyone I have known of who allows the artist to stay at their home have rules against smoking, drinking, foul language, etc. as you are staying in their home. But many artists choose to stay at a hotel in the area where the concert is located. Usually the house conert people won't mind picking you up at the hotel if it is close to where they live.