The deck looks pretty decent as far as mono-Green goes. If you would consider it,
slab hammer and
natural connection would be good choices.
Slab hammer gives some more power to your creatures while also allowing you to re-use lands that have enter the battlefield effects (Such as the dual lands from Tarkir that give you 1 life but come in tapped). Also the
natural connection pulls the land straight FROM THE DECK.......at INSTANT speed! That's insanely good in a landfall deck where you can play extra lands on your opponent's turn. Just something to consider. If you were to add RED to this deck it would become a whole new kind of monster for your opponent.