These square pots are great for medium plants and uppotting seedlings after a few months when they're grown out of their initial pots. They're higher than they are wide which it great for Anthuriums, because it leaves some room to top up the pot with soil when the plant grows a bit more. This way you can keep the aerial roots covered and they will root into the soil instead of drying up in the air.
Once the plants get rootbound in these and the stems grow higher than the top of the pots it's time to size up to Plant Pot L.
