I cultivate Phragmipediums on a substrate made of equal parts clay balls and rockwool cubes.I add to the fertilyser solution (Rain mix) 0.2 ml/1L (1/6 tsp/1gal) of seaweed extract. pH of this solution is adjusted at 6 with tap water. Mosses, weeds and even small ferns grow on the upper surface of the potting. It is very attractive but is this good or bad for the culture or for the health of the plant?