There are numerous stories in Hindu religion regarding the origin of Kusha grass. The grass is known as cotton-wool grass in English, Darbha in Hindi, Darbai in Tamil and Kusha in Sanskrit. One story regarding the origin of Kusha grass is associated with Mata Sita going back to earth.
As per the story found in the Ramayana, Mata Sita gave birth to twins after she was forced to live in the ashram of Sage Valmiki. The twins grew up and they made their father realize the injustice she had done to Mata Sita. Rama wanted to bring back Mata Sita to Ayodhya.
But Sita did not wish to go back to Ayodhya. As Sita was the daughter of Dharani, Goddess Earth, she prayed to her mother to accept her back if she was innocent. An earthquake threw open the earth and she was buried under.
When her son Kusha saw what was happening, he ran to save her but could only catch her hair. The earth closed and a few strands of hair remained in the hand of Kusha. The hairs turned into grass and were named after Kusha as he had tried to save her.
The grass is held sacred by Hindus as it is associated with Mata Sita.