Care of a hibiscus plant?

I have a hibiscus plant outside in a large planter. I live in zone four and water it regularly. The weather has been in the 60-70's during the day lately. The leaves are turning yellowish and are limp. I have not used any fertilizer. What am I doing wrong? How can I make this plant look better?

Care of a hibiscus plant?
What is the night time temp? I put my three hibiscus plants outside a little too early this year (I'm in zone 7) and the night temp fell into the high 30s/low 40s. I got a lot of foliage die off (turned yellow)





Try bringing the plants in at night, or at the very least use a frost cloth. A good watering and a bit of all purpose fetilizer should help the plants pick up.
Reply:I think the cold nights are damaging it. You can try putting plastic over it at night until the nights are 50 degrees or higher. If this is not the case, it is time for some fertilizer with iron in it or both fertilizer and supplemental iron, but if it was looking Ok and now is failing, that's not good. Foruntately, hibiscus is pretty hard and does recover from many unhappy times, so it should come around with some warmer nights and some fertilizer. Your planter might not be staying moist enough or your planter might be dark and heating up during the day - those are the other two suggestions I would have to check out.
Reply:seems like it needs more sun or is it cold at night?