Natalie,
In the beginning I kept tender plants in the greenhouse over the winter, and I did not let the temperature lower less than 65 at night. Daytime temperature with sun would reach above 90 degrees.
I used one or two oil-filled electric heater, depending on the outside temp. These heaters usually cost less than $50, and at the end of the season they cost much less. They have a thermostatic control which is a great help.
For the daylilies, I'll pay more attention during the coldest months. More recently I have overwintered hosta tissue culture plants using 42 degrees as the lowest temperature allowed. Hosta TC may not freeze the first year, after that, they will grow outdoors, some in the ground while others grow in larger pots.
This process should also give me advance growth by the time I plant them outdoors. This is a safe way to transition Florida and California plants to my much colder climate.
Gerry
