MySteel recommends placing a layer of pebbles (10cm) at the bottom of the planter first.
On top of the 10cm layer of pebbles, place a water-permeable root cloth. Then cover the root cloth with soil suitable for your type of plants.
When no pebbles and water-permeable root cloth are used, water cannot drain properly and may accumulate in the corners, which could lead to mould formation, or the material may eventually rust. These symptoms are not good for the planters.