At its best:
Fill the pot two-thirds full with multi-purpose compost. Plant the phormium at the back of the pot, with the cyclamen just in front of it and to the side so it will cascade over the edge. Plant the erica to the other side and nestle the sedum amongst them, towards the front of the pot. Fill the container with compost, to within 5cm of the rim, firming around the plants with your fingers to squeeze out any air pockets.