plot_date and multiple column subplots within matplotlib. How to change 1 column to 2 column subplot using plot_date?

I am plotting time series data in matplotlib utilising the plot_date command.

In the following code the dt_str_etc and BTOTetc refer to arrays of datetime formatted data. Part of my Code is as follows:

import matplotlib.pylab as plt
import matplotlib.dates as dates
from datetime import datetime

f,axarr=plt.subplots(nrows=9,sharex=False)

axarr[0].plot_date(dt_str_16h25,BTOT16h25,fmt='-k')
axarr[1].plot_date(dt_str_16h26,BTOT16h26,fmt='-k')
axarr[2].plot_date(dt_str_16h27,BTOT16h27,fmt='-k')
axarr[3].plot_date(dt_str_16h28,BTOT16h28,fmt='-k')
axarr[4].plot_date(dt_str_16h29,BTOT16h29,fmt='-k')
axarr[5].plot_date(dt_str_16h30,BTOT16h30,fmt='-k')
axarr[6].plot_date(dt_str_16h31,BTOT16h31,fmt='-k')
axarr[7].plot_date(dt_str_16h32,BTOT16h32,fmt='-k')
axarr[8].plot_date(dt_str_16h33,BTOT16h33,fmt='-k')

Now, the above code works. plot_date functions as you would expect and I get a nice plot with 9 subplots together with a nice looking time series...

What I want to do is to plot the above 9 plots not on one column but two columns [Essentially 2 by 5 (with one unoccupied space)]]. A multiple columned subplot. I attempted to do so using the following code:

import matplotlib.pylab as plt
import matplotlib.dates as dates
from datetime import datetime

f,axarr=plt.subplots(nrows=5,ncols=2,sharex=False)

axarr[0].plot_date(dt_str_16h25,BTOT16h25,fmt='-k')
axarr[1].plot_date(dt_str_16h26,BTOT16h26,fmt='-k')
axarr[2].plot_date(dt_str_16h27,BTOT16h27,fmt='-k')
axarr[3].plot_date(dt_str_16h28,BTOT16h28,fmt='-k')
axarr[4].plot_date(dt_str_16h29,BTOT16h29,fmt='-k')
axarr[5].plot_date(dt_str_16h30,BTOT16h30,fmt='-k')
axarr[6].plot_date(dt_str_16h31,BTOT16h31,fmt='-k')
axarr[7].plot_date(dt_str_16h32,BTOT16h32,fmt='-k')
axarr[8].plot_date(dt_str_16h33,BTOT16h33,fmt='-k')

This returns me the error:

Traceback (most recent call last):
      File "C:/Users/Charles/Google Drive/Year 4 Real/MPhys Project/Mag     Data/2007/Mag_data_2007_plot_T 25 26 27 28 29 30 31 32 33 adjusted.py", line 118, in <module>
    axarr[1].plot_date(dt_str_16h25,BTOT16h25,fmt='-k')
AttributeError: 'numpy.ndarray' object has no attribute 'plot_date'

All I have done is write "ncols=2". That is the only difference. Why can I no longer plot in this way using the plot_date command?

I have read some info on the subplot matplotlib documentation about potentiall using "add_subplot". If needs be I can re write the code using this, but I would really like to keep it as it is. Any ideas?

Many thanks for any help or thoughts provided.