Multiple values on plot_date

I am trying to plot multiple values on a date plot. plot allows for
this but plot date tells me it only takes 5 arguments. Is there a
reason for this difference? Am I using the function incorrectly?
Does anyone know of a work around? The exception is below:

Extra content at the end of the document
Traceback (most recent call last):
  File "examples/", line 68, in ?
    splot2.plot_date(dates1, y1, 'g-', dates2, y2, 'b-')
TypeError: plot_date() takes at most 5 arguments (7 given)