You can do it in multiple ways:
Here is one solution making use of tick_params
:
ax.tick_params(labelrotation=45)
Here is another solution making use of set_xticklabels
:
ax.set_xticklabels(labels, rotation=45)
Here is a third solution making use of set_rotation
:
for tick in ax.get_xticklabels():
tick.set_rotation(45)