Landscape Kurbing offers VOW's  Vehicle on Wheels which are mobile planters that can be used to plant vegetables or flowers.  They are planters that are on wheels and can be moved around your patio and are at a convenient height that makes picking vegetables or flowers very easy. They come in a variety of sizes, the most common being 2'x6'

This is our 4'x4' model and already has squash and tomatoes blooming