This idea works exceptionally well for gardens with an antique or rustic feel. Just drill a few holes for drainage at the bottom of each container -- elevated a few inches off the ground if need be -- then add soil and compost. That's it -- your plants are ready to grow!
Although a single crate, keg or barrel looks great on its own, adding multiple wooden containers to your garden makes a great theme. Try mixing and matching items of different sizes, or unify your garden with several large, strategically placed barrels.