I actually tried using eco-complete in small plastic pots. Stupidly, I did not put holes in the pots (duh). My plants looked awful in a matter of days. I quickly decided to clear several areas in the gravel where I could dump in the eco-complete, plant the plant and then cover gently with gravel to hold in place. My plants are doing well now. A consultant at my
LFS also reminded me later that eco-complete is not a complete nutritional source for the plants, but rather the porousness of this substrate is better at harboring fish waste and processing it into plant food.
I have also heard of using chemical free potting soil, but I have never tried this method. I understand there are two challenges to using potting soil: (1) finding soil that does not contain chemicals that will harm fish/put your tank chemistry totally out of whack or (2) placing the pot in the tank without adequately soaking the soil...essentially what happens is an air bubble bursts as you place the pot in the tank sending an explosion of potting soil throughout the tank!
Hope that helps...good luck