Poorly parsley

My parsley is behaving very strangely. I have had the plant for two years and it has always been very strong and bushy. Recently, the central stems have shot up very straight and green but all of the outer stems have wilted over and withered. It is in a very large pot and is inthe same spot where it has always lived. What has happened?

 

Parsley is a biennial, Sterile.
After 2 years it's done.
Time to grow a new crop.

 

Thank you, I'm sorry to see it go as it has served me very well. Quite excited about growing a new plant though :-)

 

Sorry, can I just ask, does biennial mean 'for two years'. Is there another word for once every two years - is that a relevant word to know? And, does 'biannual' exist, and presumably that means twice a year?