Question

who holds ' all the growth of our land'?which land has the poet in mind? heart of the tree

Answer 1

The planter who plants the tree holds all growth of his land
By land poet refers to the nation and country of the planter where he will plant the tree

Answer 2

on a symbolic level, the act of plantation is an act of goodness — one from which many other acts of goodness will sprout. A helpful attitude will grow among people. So, plantation is an act that inspires people to do good to others. It has the potential to grow the civilization in its true sense.

Thus the poet glorifies the act of plantation and motivate the readers in planting trees.

The land doesn't only mean our own land but all the nations and also the neighborhood✌