If you're doing water changes as you are supposed to than no, no filter. I ran a 29 with no filter for a couple of years on my back porch. And I didn't always follow my own advice. I took it down because I rearranged things in the fish house. And even there I have a few tanks with no filters.
http://www.plantedtank.net/forums/12-tank-journals/155609-all-natural-planted-soil-tank.html
http://www.plantedtank.net/forums/12-tank-journals/155609-all-natural-planted-soil-tank.html