I am very confused about the protection from frost heave. I have read that it is good to wait to mulch until after a good freeze. How hard a freeze? Is it ok to wait as long as temperatures don't get too warm after the frosts? Once there is a frost what temperatures are dangerous? I live in zone 4.
The key is to keep a steady temperature around the base/roots of a plant during freezing weather. If you mulch too soon after the first frost, you risk having a warm snap follow which will stimulate the already-warm plant to start growing again. Here in Zone 6, I usually mulch after about 10 days of consistently cold/frosty weather. If that happens early in the fall, I wait because most likely there'll be another warm spell.
Do some research for your area, or ask a nursery about the best way to handle your particular climate.