Refer to the documentation for Ticks.
You'll want to write an option such as:
Ticks->{xTicks,yTicks}
where xTicks might be Automatic, and
where yTicks might be something like:
Transpose[{label1,label2,...},{position1,position2,...}]
It can get quite tedious:
the labels need to be strings, such as "3 Jan 2013", and
the positions along the vertical axis must scale to the data range you are plotting.
