Deadheading roses is the process of removing finished flowers to redirect the life force back into the stem and leaves and to produce more flowers on repeat flowering varieties.
It is a two stage process, first cutting off the finished flower on the cluster, then when all the flowers on the cluster have gone over, cutting back to encourage new blooms and maintain the shape of the plant.
Cut off the finished flower, leaving any remaining buds / blooms on the cluster to continue to flower.
Once all the blooms on the cluster have finished flowering remove the entire flower head by cutting at a 45 degree angle (so that water runs off instead of settling on the cut) just above an outward facing set of five leaves.
If it’s a disproportionately long stem, cut back to the height of the rest of the plant to form a nice rounded shape.
As when pruning roses, cutting back to just above an outward facing bud or set of leaves, will mean that new shoots will grow outwards and not inwards back into the plant.