BUG: bar and line plots are not aligned on the x-axis/xticks

doc/source/whatsnew/v2.2.0.rst

@@ -882,6 +882,7 @@ Plotting
 ^^^^^^^^
 - Bug in :meth:`DataFrame.plot.box` with ``vert=False`` and a Matplotlib ``Axes`` created with ``sharey=True`` (:issue:`54941`)
 - Bug in :meth:`DataFrame.plot.scatter` discarding string columns (:issue:`56142`)
+- Bug in :meth:`DataFrame.plot` where bar and line plots are not aligned on the x-axis (:issue:`56611`)
 - Bug in :meth:`Series.plot` when reusing an ``ax`` object failing to raise when a ``how`` keyword is passed (:issue:`55953`)
 
 Groupby/resample/rolling

pandas/plotting/_matplotlib/core.py

@@ -1804,6 +1804,13 @@ def _kind(self) -> Literal["bar", "barh"]:
     def orientation(self) -> PlottingOrientation:
         return "vertical"
 
+    @final
+    def _set_tick_pos(self, data) -> np.ndarray:
+        if self._is_series and is_integer_dtype(data.index):
+            return np.array(data.index)
+        else:
+            return np.arange(len(data))
+
     def __init__(
         self,
         data,
@@ -1822,7 +1829,6 @@ def __init__(
         self.bar_width = width
         self._align = align
         self._position = position
-        self.tick_pos = np.arange(len(data))
 
         if is_list_like(bottom):
             bottom = np.array(bottom)
@@ -1835,6 +1841,8 @@ def __init__(
 
         MPLPlot.__init__(self, data, **kwargs)
 
+        self.tick_pos = self._set_tick_pos(data)
+
     @cache_readonly
     def ax_pos(self) -> np.ndarray:
         return self.tick_pos - self.tickoffset

pandas/tests/plotting/test_series.py

@@ -919,10 +919,7 @@ def test_plot_order(self, data, index):
         ax = ser.plot(kind="bar")
 
         expected = ser.tolist()
-        result = [
-            patch.get_bbox().ymax
-            for patch in sorted(ax.patches, key=lambda patch: patch.get_bbox().xmax)
-        ]
+        result = [patch.get_bbox().ymax for patch in ax.patches]
         assert expected == result
 
     def test_style_single_ok(self):
@@ -977,6 +974,31 @@ def test_series_none_color(self):
         expected = _unpack_cycler(mpl.pyplot.rcParams)[:1]
         _check_colors(ax.get_lines(), linecolors=expected)
 
+    def test_bar_plot_x_axis(self):
+        df = DataFrame(
+            {
+                "bars": {-1: 0.5, 0: 1.0, 1: 3.0, 2: 3.5, 3: 1.5},
+                "pct": {-1: 1.0, 0: 2.0, 1: 3.0, 2: 4.0, 3: 8.0},
+            }
+        )
+        ax_bar = df["bars"].plot(kind="bar")
+        df["pct"].plot(kind="line")
+        actual_bar_x = [ax.get_x() + ax.get_width() / 2.0 for ax in ax_bar.patches]
+        expected_x = [-1, 0, 1, 2, 3]
+        assert actual_bar_x == expected_x
+
+    def test_non_numeric_bar_plot_x_axis(self):
+        df = DataFrame(
+            {
+                "bars": {"a": 0.5, "b": 1.0},
+                "pct": {"a": 4.0, "b": 2.0},
+            }
+        )
+        ax_bar = df["bars"].plot(kind="bar")
+        actual_bar_x = [ax.get_x() + ax.get_width() / 2.0 for ax in ax_bar.patches]
+        expected_x = [0, 1]
+        assert actual_bar_x == expected_x
+
     @pytest.mark.slow
     def test_plot_no_warning(self, ts):
         # GH 55138