I tried to plot daily data from 9 variables in ggplot, but the graph I get cannot handle the date variable properly. The x axis is unreadable and its impossible to read the plot. I'm guessing there's an issue with the handling of dates.

Here's the data: https://dl.dropbox.com/u/22681355/su.csv

Here's the code I've been using:

su=read.csv(file="su.csv", head=TRUE)

meltdf=melt(su)

ggplot(meltdf, aes(x=Date, y=value, colour=variable, group=variable))+geom_line()

and here's the output:

https://dl.dropbox.com/u/22681355/output.jpg

here's the same plot done in excel, why does it look completely different?