First things first, choose the right tomato plant for the hanging planter. There is just no sense in picking a beefsteak or other large varietal. Large tomatoes generally grow on large plants and have heavy fruit. These small planters are better suited to determinate/bush forming (as opposed to indeterminate/vine growing) so that the plant can build girth rather than length below the planting bag. Also choosing container-loving cultivars like Tumbler, Jolly Elf, or Gold Nugget will ensure fruiting is prolific even on smaller plants.