At its best:
Apr, May, Jun
Drill or nail drainage holes into the base of the container, to allow water to pass through.
Add crocks to the base of the container to aid drainage.
Fill the container two-thirds with multi-purpose compost.
Plant the stipa first, in the centre of the window box, towards the back. Firm it well and ensure the rootball is level in the compost.
Add the muscari, euonymous and pansy plants around the stipa.
Fill any gaps around the plants with more compost and firm in well.
Water the window box thoroughly and allow to drain before moving to its final position.