A few hours may not be
fatal, depending on the plant species, while 12-24 hours or
longer is likely kill the same plants outright. One way to tell
is to remove the pot. Healthy roots are firm and white, while
those killed by cold are brown and mushy. If they are somewhere
in between, take them in and treat them with extra care – they
may recover, they may not.
There are a few things you can do to help them recover if they
are able. The factor most likely to kill the ones that could
recover is watering too much. Plants with no top growth use very
little water compared to plants growing well with luxuriant
foliage. Too much water when they are not using it can cause
root rot, which will certainly kill them.
Hold-off on Fertilizing
Avoid fertilizing them now or even when they first start growing
again. Fertilization pushes new growth that a damaged root
system may not be able to support. Most horticulturists
recommend withholding fertilizer for houseplants through the
winter months anyway, due to the reduced light levels – plants
generally are not putting on a lot of growth through the winter
and do not need the extra fertilizer.
Make sure plants are exposed to appropriate light levels. Those
that tolerate low light levels will not be helped by exposing
them to too much sun.