title: How to plot vertical lines at specific dates in matplotlib
body: <p>How could I add a vertical line marker to this chart at a specific date? <code>Week end</code> is the date column.</p>
  <pre><code>fig, ax = plt.subplots(figsize=(20,9))
  thirteen.plot.line(x='Week end', y='OFF', color='crimson', ax=ax)
  thirteen.plot.line(x='Week end', y='ON', color='blue', ax=ax)
  ax.set_ylim(bottom=0)
  plt.show()
  </code></pre>
  <p><a href="https://i.stack.imgur.com/qpXtX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qpXtX.png" alt="image of output" /></a></p>