My old boss in Sacramento always told me to never top a valley oak, but I saw a crew doing it last week.
He said it would just cause a ton of weak, fast-growing water sprouts and could actually kill the tree over time. I watched a company near Folsom cut the main leaders back by about eight feet on a big one, and it looked awful. Has anyone else had to explain to a client why topping is a bad idea after they saw someone else do it?
Took a client to see a topped tree from two years ago. Showed them the crowded, brittle sprouts that had grown back and explained how each cut was now a potential rot entry point. They changed their mind once they saw the long term damage up close.
Show them the real results. Seeing a topped tree a few years later is the best sales pitch against it. Those thin sprouts snap in the first ice storm, and the big cuts never heal right. It just makes a weak, ugly tree that costs more to fix later. Good on you for taking the time to show them.
Honestly, topping is called crown reduction now to make it sound better. It still creates those weak sprouts and stresses the tree like your boss said.