Learn how to build a DIY railing planter box with this tutorial!
Deck Planter for 2x4 or 2x6 Railings | Gardener's Supply
Amazon.com : The HC Companies 24 Inch Deck Railing Planter Box - Decorative Lightweight Weatherproof Plastic Plant Pot for Outdoor Balcony, Porch, Garden, Fence, White : Patio, Lawn & Garden