I wrote a couple of entries already that should help to prettify a garden (although I don’t have any ;-)) (see links below).
And I have several entries for making stuff from plastic bags, mostly bags.
So I like the idea of taking yarn from plastic bags and making plastic bag garden decorations quasi twice as much ;-))
Crocheted Plastic Wind Chime (Die ersten Windspiele) (German)
The automatic translation isn’t very convincing but I think that it doesn’t matter: simply crochet items from plastic yarn, connect them and hang them in the garden as wind chimes.