The Lechuza Balkonkasten 17 only supports smaller pots. This insert however allows you to fill the whole pot with soil and plant directly into the “Balkonkasten”. You get more volume for the plants and don't have to fiddle with different pot sizes and the “hooks” in the bottom that pull up the water through a thread. Just fill the insert with Lechuza Pon or Seramis or something similar.