I wonder if "planting" has any biological impact on the Piggies life-cycle, or if it is a ritual to honor Piggies in their society.
I know that Piggies have 3 lives:
The first-life: tiny piggies live inside the mothertree, feed on the sap.
The second-life: After they grow enough, the piggies will climb out of the mother-tree, and start living as a sentient species. Piggies like Leaf-eater, Rooter .... in the book.
The third-life: a tree. When the piggies die, they become a tree.
"Planting" is a procedure by which Piggies who earn passage to the third-life are "butchered" by his best-friend or rival. Then the butchered Piggie's corpse roots into a tree.
I wonder if "piggies" can go to third life if they are not planted, but die in other ways. Is planting just a way to honor others, or it is important for piggies life-cycle? Will something bad happen to them if they are not planted when they die?
The piggie named Human said when Ender ask them to stop the war:
"...This is very hard. Until you humans came, other piggies were-- always to be killed, and their third life was to be slaves to us in forests that we kept. This forest was once a battlefield, and the most ancient trees are the warriors who died in battle. Our oldest fathers are the heroes of that war, and our houses are made of the cowards. All our lives we prepare to win battles with our enemies, so that our wives can make a mothertree in a new battle forest, and make us mighty and great. "
From this quote, I interpret that piggies who are killed in war can go to third-life (being a tree) without planting. Because, in the quote, piggie Human said "our houses are made of the cowards" which I interpret to mean they are the enemy, and they were not planted (because planting is an honor that must be earned, not for cowards). From this evidence, I conclude that the piggies can go to third-life (became a tree) without planting.
However, when Leaf-eater think Miro is going to die when he falls off the fence, he said
"Quick!" shouted Leaf-eater. "Before he dies, we have to plant him!"
"Before he dies," said Leaf-eater. "We have to give him root."
This gave me a clue that "planting" is somehow important. It is a "must-have" procedure before someone dies? I feel like it is somehow as important as "first-aid".