At its best:
This is a heavy container, so position it where you want it before planting it up. Place polystyrene chunks or crocks in the base of the window box to aid drainage.
Fill the window box two-thirds with multi-purpose compost.
Plant up the window box, placing the taller plants at the back. Plant the ivies at the front of the box, ensuring they trail over the sides. Water the box thoroughly and allow to drain.