Hacking Boxplots
Usually the big nuisance with boxplots is accomodating the labels, which are usually too long. I suggest to keep the boxplots vertical, turn all the labels to perpendicular to axis, and increase the outer margin on the x-labels side.
x11 () par (omd = c (0, 1, 0.1, 1)) boxplot (<#...>, names = <#x_labels>, las = 2)
omd parameters are: - width (parallel to x axis), left side - width (parallel to x axis), right side - height (parallel to y axis), bottom - height (parallel to y axis), top las values are: 0: always parallel to the axis [default], 1: always horizontal, 2: always perpendicular to the axis, 3: always vertical. For a general reference, look at the par