persp() and character labels for axis

persp(x=1:4,y=1:6,z=sq3d,theta = 30, phi = 30, expand = 0.5, col = "lightblue")

(but y=days....)

of course it should be something like
persp(y=as.Date(days, format="%Y-%m-%d"),x=1:4,z=sq3d, theta=30,
phi=30, expand=0.5, ticktype="detailed", col="seagreen")

But this does not what I expected (after my experience with plot
above). ticktype="detailed" is better, but by far not the solution.
How do I add date-lables to the x-Axis of a persp() plot?
Who can help? Thanks...
Thomas