How to attach a wire planter on a deck railing
Long cable ties comes to mind.
If it was me I hold use metal strips bent into a u shape that snugly fits over the arm of the deck. Just attach the wire planter to the u shape (need to be snug to be stable).
Hi Ann: I think that most home improvement stores have holders for these types of applications. Check this Home Depot site to see what they have. I'm sure other stores would have something similar:
Think about rust and UV damage when you’re shopping.