Herb
The dreamer's weed, growing out of every neglected verge in the country.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Mugwort grows on waste ground, railway sidings and roadside verges, silver underneath and dull green above, and almost nobody notices it. That is a recent development. The Old English Nine Herbs Charm opens by addressing it directly as the oldest of herbs, and travellers across medieval Europe put it in their shoes against weariness — a use recorded so widely it must have felt obvious.
Contemporary practice knows it mainly as the dream herb. It goes into dream pillows, into pre-divination teas, into the smoke before scrying. That reputation is old but not ancient in this form: the specific dream association is much better attested in the last two centuries than in the medieval sources, which are more interested in walking, protection and women's medicine.
It is also, straightforwardly, an emmenagogue with a long history of use to bring on menstruation, and that is the reason for the warning below rather than an incidental detail. Whether it changes dreams is unproven and probably unprovable; that it deserves care is not in question.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Nicholas Culpeper, The Complete Herbal (1653)
Culpeper assigns it to Venus and is entirely candid about what it was used for: bringing down the courses, easing childbirth, expelling the afterbirth. The modern dream-herb reading has to be read alongside that, not instead of it.
Carried forward
The Nine Herbs Charm, Old English, c. 10th century
The charm addresses mugwort first, calling it the oldest of herbs and reminding it of what it accomplished at a great assembly. Whatever the poem meant by that, the plant is being spoken to as a person, which is a habit English herb-lore never entirely lost.
Carried forward
Common in contemporary practice
Kept in a dream pillow or drunk as a weak tea before sleep to sharpen recall of dreams. Practitioners report vivid results; nobody has demonstrated the effect under conditions that would rule out simply paying more attention.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.