At its best:
Add crocks to the trough to improve drainage, then fill it two-thirds full of compost mixed with water-retaining gel.
Plant the cowslips first, spacing them evenly along the length of the trough and positioning towards the back.
Add the anemones, placing them in the the gaps between the cowslips. Anemones are delicate so take care not to break them.
Water your arrangement and ensure it never dries out. Deadhead faded cowslips to encourage new blooms.