The passuk, in Devarim 20:19, says "For a man is like the tree of the field". This comparison has led to the minhag based on kabbala of not cutting a young boy's hair until he is 3 years old and then cutting the hair but leaving the peyos. This is because man is like a tree, and orla cannot be eaten for the first 3 years of the tree's life, so a boy's hair cannot (or should not) be cut for the first three year's of the child's life.

The connection is actually deeper than that, as evidenced by a recent incident with Rav Chaim Kanievsky.

Actualic is reporting on an elderly man that came to Rav Chaim Kanievsky relating that he himself had only had one child, a son, that was born to him and his wife after many years of waiting..the son married at a bit of an older age, but now he too has been waiting a few years without child.

The elderly man related that while trying to figure out what they might have done to deserve such troubles and difficulties in this specific issue, he remembered that recently in a shiur he learned about a gemara that says that someone who does not observe the laws of orla in chutz laaretz will not have grandchildren. The man says he realized that and was shocked because it seems to be speaking to him directly. The man recalled an incident in which many years prior a non-religious relative abroad had asked him about eating the fruits of the tree he was growing, and he had told this fellow that the need to wait 3 years for orla only applies in Israel so he would be able to eat it right away without waiting. Now he realizes that this was a mistake and perhaps this had caused his punishment of no grandchildren and such difficulty in conceiving...

He asked Rav Chaim what he could do, if anything, to make up for it and not be liable as per the gemara's discussion.

Rav Chaim Kanievsky responded that he is right that that had been a mistake and is a problem, but tshuva is always an option. Rav Chaim told him that if he does tshuva, with God's help he will have grandchildren...

He obviously already regrets his error, and now that he knows orla applies abroad he probably wont make that mistake again, if it would ever even come up again, so perhaps his tshuva has already been done. I wonder if he has to do something more specific in this case. Anyways, I wish him well and hope he will be blessed with wonderful grandchildren.