Rich Howard of CT Daylilies (hardiness zone 6a) relates an unintended hardiness experiment:

"We grow many daylilies in pots for several reasons. I originally started doing so in
order to bring some to the Farmer's Market to sell when in bloom. I also now have a
greenhouse so many go into the greenhouse late in the year after they have had a bit
of chilling. I bring the Evergreens and Semi Evergreens in around Thanksgiving and
the Dormants around Christmas.

The greenhouse was supposed to be constructed by Dec. 2003. I had various
sub-contractors involved as well as a couple of permits I needed. Despite starting the
process in July the project did not get completed until Jan 2004. This might not have
been a problem except I had left the pots I was to put inside uncovered and Jan. was
the coldest month in 60 years. We had 6-8 days of sub-zero temperatures. I have
never estimated the value of the hundreds of pots I lost.

However, I have around 40 pots that underwent the cold and the plants lived .Here is
the list of those stalwarts:

BAT SIGNAL
CREATURE OF THE NIGHT
DANCING CRAB
EAGER BEAVER
ENVY ME
FAT MAN
GATES OF PEARL
GOLD ELEPHANT
GREY WITCH
JOSEPH'S COAT
KARATKEA
KAREN'S CURLS
LEE REINKE
LOBO LUCY
MEMORY JORDAN
MILADY GREENSLEEVES
NOTIFY GROUND CREW
NUCLEAR MELTDOWN
OLD KING COLE
OLIVES ODD ONE
ORCHID MAJESTY
PERSIAN RUBY
STELA DE ORO
TROPICAL DEPRESSION
TWIST AGAIN
TYROLEAN TRAESURE
UFO
VARIEGATED KWANZO(some)
VICTORIAN RIBBONS
VOLCAN FUEGO
WATCHYL CYBER SPIDER
WESTWARD WIND
WOODSIDE ROMANCE"