Yggdrasil as a cosmic tree is sometimes called an ash and sometimes a yew. A clue to the correct name may be another Norse word for yew which is a needle of ash.
Yggdrasil, otherwise known as the World Tree, grows out of the past, lives in the present and reaches toward the future. It nourishes all spiritual and physical life. It's roots reach into all the nine worlds of Norse Myth and Religion. And it's boughs hang above Asgard.
The Spring of Hverglmir (Roaring Cauldron) is the source of all water and rises up through the tree Yggdrasil to all the worlds. It lies at the lowest level of the nine worlds and has one of the Yggdrasil's roots deep within it.
Yggdrasil has three main roots which hold everything togethr. One root reaches into the Well of Urd in Asgard, another into the fountain of Mimir in Midgard, and the third into the Spring of Hvergelmir in Hel. At Hvergelmir is the watchman Ivaldi and his sons who defend Hel against the Storm Giants.
The World Tree is constantly under attack by evil creatures. In Niflheim, the dragon Nidhogg continually chews on it's root. In Midgard, four giant hawks eat the buds and the leaves. Age rots it's sides, and many serpents of the dark underworld attack it's wood. But the Norns sprinkle it each morning with water from Urd's fountain of life.
Odin and Freya Bless,