What is the ruling on adorning a guest's neck with a flower garland upon their arrival?

There is no harm in adorning a guest with flowers to honor and welcome him. Islam encourages honoring guests with whatever permissible means are available. The Prophet, peace and blessings be upon him, said: "Whoever believes in Allah and the Last Day, let him honor his guest," and he also said: "Whoever believes in Allah and the Last Day, let him treat his guest generously."