A big thanks to RuthC above, she had the answer. The following is what I used.
df_cols = ['WC_015', 'WC_030', 'WC_046', 'WC_061', 'WC_076', 'WC_091',
'WC_107', 'WC_122', 'WC_137', 'WC_152', 'WC_168', 'WC_183', 'WC_213',
'WC_244', 'WC_274', 'WC_305', 'WC_366', 'WC_427', 'WC_488', 'WC_518']
fig, axs = plt.subplots(20, 1, figsize=(50,30)) #, sharex=True, sharey=True) 20
for k, col in enumerate(df_cols):
df[col].plot(ax=axs[k])
axs[k].annotate(df_cols[k], xy=(.01, .115), xycoords='axes fraction', fontsize=15, rotation=90, color='red')
fig.subplots_adjust(hspace=0)
plt.suptitle ('Volumetric Moisture Content', fontsize=40, y=.91)
plt.ylabel('Volumetric Moisture Content (m3/m3)', fontsize=30, y=10.0)
plt.xlabel('Date', fontsize=30)
plt.savefig('Moisture_Content_Plots.pdf', dpi=100, bbox_inches='tight')
