I inherit plants at work... Three years ago I started caring for this hibiscus and it was just a little stem of a thing, everyone had given up on it. Now I am starting to worry that it is going to outgrow it's windowsill! My question is: is it possible to encourage it to branch out more vs. just growing up and up and up? It is only the tallest stalk that seems to grow, the other two branches put out a new leaf occasionally, but not very often.

It has two flower buds on the tall stalk at the moment (which is the only spot that blooms), so I don't want to cut it back. Here is a bloom from the summer:

Actually... looking at that photo, I can tell the whole plant has grown a lot as that small branch that's kind of hanging down sure doesn't look like that anymore!

Further info: it's in a south facing window and I water it twice a week. I'm certain that it needs to be repotted as I have never done it and who knows how long it was hanging around before I got here.