diff --git a/pandas/plotting/_core.py b/pandas/plotting/_core.py
index b15c5271ae321..3e186b7e4aaee 100644
--- a/pandas/plotting/_core.py
+++ b/pandas/plotting/_core.py
@@ -561,12 +561,14 @@ def _get_xticks(self, convert_period=False):
             if convert_period and isinstance(index, PeriodIndex):
                 self.data = self.data.reindex(index=index.sort_values())
                 x = self.data.index.to_timestamp()._mpl_repr()
-            elif index.is_numeric():
+            elif (index.is_numeric() or
+                  index.inferred_type in ['string', 'unicode']):
                 """
                 Matplotlib supports numeric values or datetime objects as
                 xaxis values. Taking LBYL approach here, by the time
                 matplotlib raises exception when using non numeric/datetime
                 values for xaxis, several actions are already taken by plt.
+                Matplotlib also supports strings as xaxis values.
                 """
                 x = index._mpl_repr()
             elif is_datetype:
diff --git a/pandas/tests/plotting/test_frame.py b/pandas/tests/plotting/test_frame.py
index 3d25b0b51e052..6dcd342b94a47 100644
--- a/pandas/tests/plotting/test_frame.py
+++ b/pandas/tests/plotting/test_frame.py
@@ -139,6 +139,28 @@ def test_plot(self):
             result = ax.get_axes()  # deprecated
         assert result is axes[0]
 
+    # GH 18726
+    def test_two_plots_with_x_str(self):
+        x1, y1 = ['a', 'b'], [1, 2]
+        x2, y2 = ['b', 'a'], [4, 3]
+        df1 = pd.DataFrame(y1, index=x1)
+        df2 = pd.DataFrame(y2, index=x2)
+        ax = None
+        ax = df1.plot(ax=ax)
+        ax = df2.plot(ax=ax)
+
+        line1, line2 = ax.lines
+
+        # xdata should not be touched (Earlier it was [0, 1])
+        tm.assert_numpy_array_equal(line1.get_xdata(), np.array(x1),
+                                    check_dtype=False)
+        tm.assert_numpy_array_equal(line1.get_ydata(), np.array(y1),
+                                    check_dtype=False)
+        tm.assert_numpy_array_equal(line2.get_xdata(), np.array(x2),
+                                    check_dtype=False)
+        tm.assert_numpy_array_equal(line2.get_ydata(), np.array(y2),
+                                    check_dtype=False)
+
     # GH 15516
     def test_mpl2_color_cycle_str(self):
         # test CN mpl 2.0 color cycle