Lavender, chamomile, lemon balm and catnip carry the aromatics people reach for when they want to slow down. We will not tell you what the compounds do; what we will say is that the ritual is the point, and the ritual works better with a living plant in it.
Cut a few sprigs, crush them between your fingers, smell your hands, put the kettle on. That whole sequence takes two minutes and it is unavailable from a box.