I've been mulching for 3-4 years on my trees since I can't always get there to water them. I have not had any issues. Like said earlier though, stay a few inches off the trunk. I also used moisture mizer when i planted them. This combination works well. The trees that are 3-4 years old the mulch has mostly broken down, debating whether to add more as these should have a nice strong root system in place by now. Most of the trees are standard rootstock, which should also help on that front with a bigger and deeper root system.