In the Poetic Edda, the tree is mentioned in the three poems Völuspá, Hávamál, and Grímnismál.
"Norns" (1832) from Die Helden und Götter des Nordens, oder das Buch der Sagen.
In the second stanza of the Poetic Edda poem Völuspá, the völva (a shamanic seeress) reciting the poem to the god Odin says that she remembers far back to "early times", being raised by jötnar (giants), recalls nine worlds and "nine wood-ogresses" (Old Norse nío ídiðiur), and when Yggdrasil was a seed ("glorious tree of good measure, under the ground"). In stanza 19, the völva says:
An ash I know there stands,
Yggdrasill is its name,
a tall tree, showered
with shining loam.
From there come the dews
that drop in the valleys.
It stands forever green over
In stanza 20, the völva says that from the lake under the tree come three "maidens deep in knowledge" named Urðr, Verðandi, and Skuld. The maidens "incised the slip of wood," "laid down laws" and "chose lives" for the children of mankind and the destinies (ørlǫg) of men. In stanza 27, the völva details that she is aware that "Heimdall’s hearing is couched beneath the bright-nurtured holy tree." In stanza 45, Yggdrasil receives a final mention in the poem. The völva describes, as a part of the onset of Ragnarök, that Heimdallr blows Gjallarhorn, that Odin speaks with Mímir's head, and then:
the ash, as it stands.
The old tree groans,
and the giant slips free.
Odin sacrificing himself upon Yggdrasil (1895) by Lorenz Frølich.
In stanza 34 of the poem Hávamál, Odin describes how he once sacrificed himself to himself by hanging on a tree. The stanza reads:
I know that I hung on a windy tree
nine long nights,
wounded with a spear, dedicated to Odin,
myself to myself,
on that tree of which no man knows
from where its roots run.
In the stanza that follows, Odin describes how he had no food nor drink there, that he peered downward, and that "I took up the runes, screaming I took them, then I fell back from there." While Yggdrasil is not mentioned by name in the poem and other trees exist in Norse mythology, the tree is near universally accepted as Yggdrasil, and if the tree is Yggdrasil, then the name Yggdrasil directly relates to this story.
In the poem Grímnismál, Odin (disguised as Grímnir) provides the young Agnar with cosmological lore. Yggdrasil is first mentioned in the poem in stanza 29, where Odin says that, because the "bridge of the Æsir burns" and the "sacred waters boil," Thor must wade through the rivers Körmt and Örmt and two rivers named Kerlaugar to go "sit as judge at the ash of Yggdrasill." In the stanza that follows, a list of names of horses are given that the Æsir ride to "sit as judges" at Yggdrasil.
In stanza 31, Odin says that the ash Yggdrasil has three roots that grow in three directions. He details that beneath the first lives Hel, under the second live frost jötnar, and beneath the third lives mankind. Stanza 32 details that a squirrel named Ratatoskr must run across Yggdrasil and bring "the eagle's word" from above to Níðhöggr below. Stanza 33 describes that four harts named Dáinn, Dvalinn, Duneyrr and Duraþrór consume "the highest boughs" of Yggdrasil.
In stanza 34, Odin says that more serpents lie beneath Yggdrasil "than any fool can imagine" and lists them as Góinn and Móinn (possibly meaning Old Norse "land animal"), which he describes as sons of Grafvitnir (Old Norse, possibly "ditch wolf"), Grábakr (Old Norse "Greyback"), Grafvölluðr (Old Norse, possibly "the one digging under the plain" or possibly amended as "the one ruling in the ditch"), Ófnir (Old Norse "the winding one, the twisting one"), and Sváfnir (Old Norse, possibly "the one who puts to sleep = death"), who Odin adds that he thinks will forever gnaw on the tree's branches.
In stanza 35, Odin says that Yggdrasil "suffers agony more than men know", as a hart bites it from above, it decays on its sides, and Níðhöggr bites it from beneath. In stanza 44, Odin provides a list of things that are what he refers to as the "noblest" of their kind. Within the list, Odin mentions Yggdrasil first, and states that it is the "noblest of trees".