How to Propagate allium 'Gladiator'?
Propagate by offsets which can be carefully detached by lifting the bulb after flowering has finished. See bulb propagation

allium 'Gladiator' · Allium 'Gladiator'
Grow in full sun and fertile well-drained soil. It is best to grow in containers where garden soil is heavy clay and prone to saturation over winter. See allium cultivation
Propagate by offsets which can be carefully detached by lifting the bulb after flowering has finished. See bulb propagation