She was responsible for the growth of all the fruits and growing things of Arda.
Beginning in the Years of the Lamps during the Spring of Arda, she planted and caused to grow the first growing things of the world (trees and plants), which she had long prepared. At first, just as every other thing in the world that the Valar nurtured and cared for, these things prospered and thrived for a time. Melkor, however, had his own plans and they involved taking the world from his brethren and ruling it for himself. From his great fortress of Utumno in the far north, he sent forth his poisons into the veins of the world blighting the Spring of Arda. Then the things of Yavanna fell sick and rotted and soon after Melkor assaulted and destroyed the Two Lamps, breaking the world.
Afterwards, the Valar relocated to the continent of Aman where they created the Two Trees - the only light in the whole world at that time. Middle-earth was left in darkness, and the living things that survived were put into a great sleep by Yavanna until the rise of the Sun and the Moon many thousands of years later.
After Eru allowed Aulë's creations, the Dwarves, to survive, Yavanna feared that they would cut down all the trees in Middle-earth. Eru answered her plea by creating the Ents to protect and shepherd the trees.
In the Song of the Ainur, Yavanna sang of branches of great trees that would receive the rain of Manwë and Ulmo, and some trees sang to Ilúvatar. This is said to be the conception of the Shepherds of the Trees. Her thought also met with Manwe's, setting the arrival of the Great Eagles.
In the beginning of days, Yavanna planted the first seeds of Arda and watched over the Olvar and all growing things. As Morgoth was corrupting her beloved creatures, she contended with him and supported all the plans against him. After his expulsion from Arda she planted the seeds that she had long devised and life came to Middle-earth during the Spring of Arda, although in the beginning no flowers bloomed. When the Two Lamps were destroyed much of the life on Middle-earth slumbered in the Sleep of Yavanna that lasted until the rising of the Moon and the Sun.
After the destruction of the Two Lamps the Valar withdrew to Aman and created Valinor. Upon the green mound of Ezellohar, Yavanna sat and sang while the other Valar sat and listened. Her song, with the aid of the tears of Nienna brought forth the Two Trees, her greatest creation, which gave light to the land. However, Yavanna did not forsake the Outer Lands; at times she would come there and heal the hurts of Morgoth and urged the other Valar to wage war on him before the Awakening of the Elves.
After Eru allowed Aulë's creations, the Dwarves, to survive, Yavanna feared that they would cut down all the trees in Middle-earth. Aulë, in reply, told her that even Elves and Men, the true Children of Ilúvatar would have need of her trees as well. Yavanna lamented to Manwë, questioning whether anything she had made would be free from the dominion of others. Manwë brought her concerns before Ilúvatar in prayer, and Eru did indeed have pity upon Yavanna: He answered her plea by creating the Ents to protect the trees.
When the Elves built Tirion upon Tol Eressëa Yavanna fashioned the tree Galathilion, a lesser image of Telperion, for the court beneath the Mindon.
After the destruction of the Two Trees Yavanna examined their remains and told the other Valar that if she could use the light of the Silmarils she could heal them. This light she was denied by the will of Fëanor. Doing what she and Nienna could, they managed to bring forth one silver flower from Telperion and one golden fruit from Laurelin. She gave these to her husband Aulë, who fashioned vessels for them and thus created the Moon and the Sun.
For the Men who had stood with the Valar in the War of Wrath the land of Andor was raised by Ossë, established by Aulë, and enriched by Yavanna. When the Edain came to this island they created the realm of Númenor. In the later centuries, when the Valar decided to send emissaries to the mortal lands, Yavanna begged the Maia Curumo to take her servant, Aiwendil, with him.
