Beware! You don't specify your plant sufficiently. Your temps are on the
borderline of too cold for many cultivars. But, if for example you have a
cultivars based on H. syriacus you are a long way from being too cold at
40F for a plant that take freezing temps with ease. Make sure at your
current tempertures it does not suffer water-logging which almost certainly
will kill it by spring. If you can cover it with a wigwam of fleece it will
surely be more likely to pull through and come back into growth with greater
ease (earlier than it would otherwise next year).
Regards
Mike Gilmore
WinsfordWalledGarden, SW England,
USDA Zone9a

"Zemedelec" wrote in message
...
40 degree nights and my variegated hibiscus is still putting out a blossom
or
two. Last winter a freeze killled it to the ground, but during summer it
grew
three feet and proportionately wide. Could the gradually cold, but not
freezing temps be hardening it off?
zemedelec