THIS MOUTH DOES 3 THINGS. 1ST IT ALLOWS AN ENTRY TO FEED THE MICROS WITH YOUR LEFTOVERS/GRASS/ETC. 2ND IT GIVES THE SOIL NITROGEN AS THE LEFTOVERS DECOMPOSE, ACTING AS A NATURAL COMPOSTING SYSTEM. 3RD IT ALLOWS WATERING INTO THE SOIL ; NOT ON TOP. IT SEALS ENOUPH TO ALLOW AIR WITHOUT ALLOWING FLIES TO ENTER AND SMELLS TO LEAVE ... THEREBY CREATING THAT NATURAL, EFFICIENT ECOSYSTEM.