I would like to add this information from Cricket Hill email that LG posted in another thread.
"Frost Hardiness of New Growth
New growth on peonies is quite freeze tolerant. If you have less than 3'' of new growth, there is no need for concern, even if temperatures dip down into the teens (as is forecast for this weekend here in Connecticut). Once significant new growth begins, damage will be avoided so long as temperatures do not go below the low 20s. If you do feel the need to protect new growth, and upturned pail or barrel is often the best protection against overnight lows. For larger tree peony specimens, creating a teepee with wooden stakes and wrapping this with a tarp or agricultural row cover (reemay) is a good option. Just to reiterate, these measures should only be considered if there is a significant amount of new growth and the temperatures are going into the low 20s."
If anyone has personal experience with regards to freeze damages, please record the tree peonies' growths and the temps at which the damages occur here.
