The plant is smart. It sheds the lower leaves as it grows because it knows that when bud making time comes, that it wont be getting lots of light down there and bud production will suck down there too. Giving less chance of the plant eventually getting pollenated by some by plant airborn jizz. So the bottom leaves drop and the plant puts more energy into the top where it thinks the jizz loads will be flying.
Another reason that plants will lose lower leaves that you may be guilty of is improper lighting. If the lights your using arent for growing, or are weaker than they should be, then the plant can lose the lower leaves. If your plants engine (the light) isnt puting out enough energy then the plant realizes that not all of itself can survive, so once again it focuses on the top of the plant in hopes that it recieves a giant bukkake of plant semen one day, so it drops the lower leaves.
So if you want the plant to do well id grab a seven gallon smart pot. A drip catcher. A 400 w hps light. Some easy one part nutrients and a bottle of calmag. And put that thing in a closet that you dont use. All that stuff will cost you around 400 bucks but youll grow that (well maybe not off that particular plant) in one grow. Then your set up cost is paid for and everything else is FREE weed. You can buy single feminised seeds online for like ten bucks or less and away you go.