Penny,

For starters an attentive, well informed audience, if only one person in her garden, has to be some reward to the musicians at work. God knows that can be hard enough to find when playing in a pub. As you point out, it's not your venue in which they are playing, so perhaps when they're finished you can call across the garden wall and invite the players over for a pint and a little food. Who knows, you may make some friends and a party might break out. It sounds as though the pub isn't a good neighbor, but I envy you your situation just now. Keep us posted.

Cheers, Dave