Amazon.com : Adjustable Flower Pot Rack Holder Plant Stand - Expands 14"-27" to accomodate Multiple flowerpots, Hanger Hooks fit Almost Any Balcony, Fence or Deck Railing up to 6" Wide - Steel
HONEY JOY 6 Potted Plant Stand Rack 100% Pine Wood Flower Pot Holder Shelf Multi-Layer Flower Stand Wheels (6-Tier) TOPB006548 - The Home Depot
Learn how to build a DIY railing planter box with this tutorial!