Stop watering. I have found that lack of water puts plants into dormancy so that even a blip in warm temp will not wake them up. The trick is to keep them dry enough to cause sleep but not so dry that they wilt and die. I end up adding half a cup of water about once a month - or on every major winter holiday. (Halloween, Thanksgiving, Christmas, Valentines Day, St. Pat's Day) A lack of light also helps to ensure dormancy so keep away from any windows in your garage. Sometimes no matter what you do a tender plant is just going to give up in a winter climate. Look at it as a learning experience and keep experimenting with different ways to overwinter different tender plants. Last winter I just put my Abutilon flowering maple under the eaves on the shaded side of the house and it lost all its foliage and looked dead. In spring I saw a sprout, watered and fertilized and I have a healthy blooming Abutilon that I enjoyed all summer. Maybe this winter it will get so cold that this easy method will not work. Blame Mother Nature not yourself and Keep Growing, Marianne Binetti