R - Converting Column to Date

In my sleep data, I have a date column that was originally a character type. When plotted in ggplot(), it was listing every date in the x axis, making the labels very crowded.

Then I added the following code

dailytotals$EndDate <- as.Date(dailytotals$EndDate , "%m-%d-%Y")

which converted it to a date type. Then ggplot automatically created tick marks and labels every 15 days (for data that spans two months.

Note that the %Y (capitalized) recognizes a four digit year where %y (lower case) recognizes a two digit year.