A square pot with the same width as a round pot with that same diameter will have more potting media volume. So, you can fit a bigger root ball in the same basic area/volume of your growing area with a square pot. I have switched everything to Rand air cone pots both for this reason and for what seems like a better aeration scheme. If you can control algae growth (I do it with hydrogen peroxide-type solutions) I have decided I actually do like seeing the root growth through the more translucent plastic.
I totally agree with terryros. I use clear round pots too but if the plant fits an aircone pot then that is what I use. Square will not tip over as easily if you have a top heavy plant and they can pack in easier because of straight sides if you are space challenged. Sometimes the plant needs more spread anyways but it does help. It does hole more media than the same size round pot so be careful not to over pot some plants.
Terryros, what's Hydrogen Peroxide treatment you use to kill the algae?
---------- Post added at 05:08 AM ---------- Previous post was at 05:05 AM ----------
It seems like with round pots you get roots growing around and around. With square pots I don't see roots as long. Theoretically an orchid should put out as much root to sustain the plant so they should be the same.
I use what is now called Biosafe Disease Control (formally Zerotol) that you can get from First Ray's. This is the concentrate and I mix 10-15 ml in a total volume of 250-300 ml in a spray bottle. You can spray the surface of the pot periodically to keep surface algae under control. I drip some down the sides of an Aircone pot if I am seeing some build up there. Algae only grows where light gets in. If you have your pots fairly close together, there isn't that much light getting in when I am using all overhead LED lighting.