The url to copy and paste is

http://peonies.org/freezereport2007.html

My herbaceous ones show no visible damage.

With my tree peonies, the ones that leaves out have the
most damage. The ones that are just starting show no
damage.

After the second cold day, one of my tree peony that
leaves out completely looked bad. The leaves drooped
and looked frozen even after the sun's out. I went
and cover all of my tps.
Some I covered w/ new mulch, some I cover w/ big container w/ holes (like the recycling
bins). I took the plastics off during the
day but left the mulch on. After several days,
I noticed that the plastic coverings didn't seem to
make any difference in protecting the leaves of the tps.
Some just seem hardier than others. I figure since
they have holes, the temp got really cold anyways, the plants
just didn't suffer from the strong wind that we
have had here. I removed all the mulch yesterday as the weather
was warming up and found 3 of them that leaved out and
mulched seem completely gone. As of today, the ones that
looked damaged but not mulches seem to be looking better.

My tps are all very young. If they don't flower this
year, I wouldn't know whether age or weather was the factor.
My primary goal was to protect the plants so they survive,
flowers are secondary.

In conclusion, if I had to do it again, I would not
cover the plants w/ mulch. I probably would just
provide some wind protection and let nature take its
course. My protection seem not to make any difference,
in the best case :(

By the way zones really are only a measure of the temperatures not growing conditions. Too many people rely on them for plant purchases. My friends in the west live in zone 7-8 but can not raise some of the plants designated for that zone because they have strong salt breezes.