title: X-axis not matching when plotting two dataframes in one figure
body: <p>I'm trying to plot two dataframes in a single graph sharing x-axis.
  One dataframe fits perfectly into the graph, but the other one ends in the middle of the graph.
  Each dataframe df1 and df2 looks like this:</p>
  <pre><code>          dates  n_pos  n_neg
  289  2021-12-27      2    293
  290  2021-12-28      2    259
  291  2021-12-29      0    190
  292  2021-12-30      0    163
  293  2021-12-31      1     82
            dates  n_pos  n_neg
  147  2021-12-27      3     11
  148  2021-12-28      1     10
  149  2021-12-29      3     21
  150  2021-12-30      1      7
  151  2021-12-31      1      9
  </code></pre>
  <p>I found out that the reason lies in the difference in number of rows of the dataframe. One has 293 rows and the other has 151 rows. Still, I don't know how to fix it. The plotting code is as follows.</p>
  <pre><code>    df1['dates'] = pd.to_datetime(df1['dates'])
      df2['dates'] = pd.to_datetime(df2['dates'])
      ax = df1.plot(x='dates', y=['n_pos', 'n_neg'], kind='line', use_index=True, sharex=True, title=figname.replace(&quot;_&quot;, &quot; &quot;)+&quot; Tweets&quot;, figsize=(15,10), legend=True, fontsize=12)
      df2.plot(ax=ax)
      ax.set_xlabel(&quot;Dates&quot;, fontsize=12)
      ax.set_ylabel(&quot;Num of Sentiments&quot;, fontsize=12)
      ax.legend(['# of Positive Provax Tweets', '# of Negative Provax Tweets', '# of Positive Antivax Tweets', '# of Negative Antivax Tweets'])
      plt.show()
  </code></pre>
  <p>After changing the date column to datetime object,
  The updated resulting graph looks like this.
  The dates starts from Jan 2020 and ends by the end of the last year.
  I'm sure I don't have 1970s data and don't know why it plots on screen! And what happens to the y-axis?</p>
  <p><a href="https://i.stack.imgur.com/bBLrS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bBLrS.png" alt="enter image description here" /></a></p>