#for the minor ticks, use no labels; default NullFormatter
From this you might guess ax.xaxis.set_minor_formatter.
Yeay! Thanks for these pointers; it now works great.
Something that confused me is that for a log plot,
returns a NullFormatter (you would think it would return a LogFormatter).
This made me think that both major and minor ticks were handled by the
major formatter (which distinguishes them based on it's internal
Anyway, thanks again for your help.