So the Zoramites asked Alma how to the nourish the tree and this chapter is his answer. So simple. Pray and put your trust in Christ who will come to redeem them.
Implied in this simple answer are a couple of things. First, the act of prayer implies an answer. Examples are given. God answers prayers. Often the answer comes by God doing something. I think the entire Book of Mormon teaches that more often, God requires something of us. In this case this comes in instruction and commandment and requires obedience (the second implication) of us before it can be efficacious. This obedience represents the 'good works' Alma speaks of.
Sometimes obedience requires something difficult like Nephi returning to Jerusalem for the Brass Plates. Other times it requires merely trusting in the Lord as in Moses's requirement that the Israelites look upon the Brazen Serpent.
My experience has been that most of us would rather go fetch the plates of brass than gaze upon the brazen serpent. We want to be doing because we have ourselves convinced that we can influence the outcome with the interjection of the 'arm of the flesh'. Somehow we think that going and doing are better than becoming and being. We want to be in the driver's seat, in charge. It was that mistaken notion that kept me in the bonds of addiction for 45 years, even as an active church member. It was not until I let God drive and put my absolute trust in Him that I was rescued from my bondage.
Every time I tell my story someone complains, "That can't be right?" "Are you telling me that God will save me without keeping the commandments?" "We are expected to keep the commandments!" Some how they think that those who looked upon Moses' serpent got off easy while the others who busied themselves opening wounds and sucking out poisons were
doing the right and expedient thing. Some how they can't understand that looking upon the brazen serpent represented putting your trust in the Lord which is among the foremost of commandments. Besides those who pray in faith more typically ask the Lord what he would have them do, rather than directing Him around the Heavens and the universe. They do this because they no longer fear what He would have them do. And then they go out and do that which He reveals. Guess what, that means they go out and go Home Teaching, paying tithing, serving their neighbors and so on. They are obedient, but they credit God instead of themselves not only with the blessing of forgiveness and remission of sins, but with the good that permeates what they do. When people come to this point their tree is fully grown and bearing fruit in abundance.