scale_x_date （x_label as year-month-day）

Position Scales For Date/Time Data

These are the default scales for the three date/time class. These will usually be added automatically. To override manually, use scale_*_date for dates (class Date), scale_*_datetime for datetimes (class POSIXct), and scale_*_time for times (class hms).

ggplot(meat, aes('date','beef')) + \    geom_line() + \    scale_x_date(labels = date_format("%Y-%m-%d"), breaks='10 years')