diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -3901,10 +3901,10 @@ def dopatch(xs, ys, **kwargs):
         N = len(bxpstats)
         datashape_message = ("List of boxplot statistics and `{0}` "
                              "values must have same the length")
-        # check position
         if positions is None:
             positions = list(range(1, N + 1))
-        elif len(positions) != N:
+        positions = self.convert_xunits(positions)
+        if len(positions) != N:
             raise ValueError(datashape_message.format("positions"))
 
         # width
@@ -6048,7 +6048,7 @@ def pcolormesh(self, *args, alpha=None, norm=None, cmap=None, vmin=None,
 
         # convert to one dimensional arrays
         C = C.ravel()
-        coords = np.column_stack((X, Y)).astype(float, copy=False)
+        coords = np.column_stack((X, Y)).astype(float)
         collection = mcoll.QuadMesh(Nx - 1, Ny - 1, coords,
                                     antialiased=antialiased, shading=shading,
                                     **kwargs)

diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
@@ -4,6 +4,8 @@
 
 import datetime
 import logging
+import numbers
+import warnings
 
 import numpy as np
 
@@ -1477,9 +1479,14 @@ def have_units(self):
         return self.converter is not None or self.units is not None
 
     def convert_units(self, x):
-        # If x is already a number, doesn't need converting
+        # If x is already a number, doesn't need converting, but
+        # some iterables need to be massaged a bit...
         if munits.ConversionInterface.is_numlike(x):
-            return x
+            if isinstance(x, list) or isinstance(x, numbers.Number):
+                return x
+            if issubclass(type(x), np.ma.MaskedArray):
+                return np.ma.asarray(x)
+            return np.asarray(x)
 
         if self.converter is None:
             self.converter = munits.registry.get_converter(x)

diff --git a/lib/matplotlib/dates.py b/lib/matplotlib/dates.py
@@ -419,6 +419,11 @@ def date2num(d):
             return _dt64_to_ordinalf(d)
         if not d.size:
             return d
+        if hasattr(d, 'dtype'):
+            if ((isinstance(d, np.ndarray) and
+                    np.issubdtype(d.dtype, np.datetime64)) or
+                    isinstance(d, np.datetime64)):
+                return _dt64_to_ordinalf(d)
         return _to_ordinalf_np_vectorized(d)
 
 

diff --git a/lib/matplotlib/testing/conftest.py b/lib/matplotlib/testing/conftest.py
@@ -91,17 +91,8 @@ def pd():
     pd = pytest.importorskip('pandas')
     try:
         from pandas.plotting import (
-            register_matplotlib_converters as register)
+            deregister_matplotlib_converters as deregister)
+        deregister()
     except ImportError:
-        from pandas.tseries.converter import register
-    register()
-    try:
-        yield pd
-    finally:
-        try:
-            from pandas.plotting import (
-                deregister_matplotlib_converters as deregister)
-        except ImportError:
-            pass
-        else:
-            deregister()
+        pass
+    return pd
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -5422,6 +5422,18 @@ def test_pandas_bar_align_center(pd):
     fig.canvas.draw()
 
 
+def test_pandas_data_unpack(pd):
+    # smoke test for all these different calling methods.
+    dates = [datetime.datetime(2018, 7, i) for i in range(1, 5)]
+    values = np.cumsum(np.random.rand(len(dates)))
+    df = pd.DataFrame({"dates": dates, "values": values})
+    plt.plot(df["dates"].values,  df["values"])
+    plt.scatter(df["dates"],  df["values"])
+    plt.plot("dates", "values", data=df)
+    plt.scatter(x="dates", y="values", data=df)
+    plt.draw()
+
+
 def test_axis_set_tick_params_labelsize_labelcolor():
     # Tests fix for issue 4346
     axis_1 = plt.subplot()

diff --git a/lib/matplotlib/tests/test_dates.py b/lib/matplotlib/tests/test_dates.py
@@ -616,6 +616,16 @@ def tz_convert(*args):
     _test_date2num_dst(pd.date_range, tz_convert)
 
 
+def test_dateboxplot_pandas(pd):
+    # smoke test that this doesn't fail.
+    data = np.random.rand(5, 2)
+    years = pd.date_range('1/1/2000',
+                          periods=2, freq=pd.DateOffset(years=1)).year
+    # Does not work
+    plt.figure()
+    plt.boxplot(data, positions=years)
+
+
 def _test_rrulewrapper(attach_tz, get_tz):
     SYD = get_tz('Australia/Sydney')