the Messenger of Allah said: "For what is watered by the heavens and steams, the Ushr is due, and for what is watered by irrigation, half of the Ushr."
Jami` at-Tirmidhi Book 7, Hadith 23
← Previous Hadith Mu'adh had written to the Prophet to ask him about greens - which is "herbs" - so he (pbuh) said, "There is nothing due on them."

Jami` at-Tirmidhi Book 7, Hadith 22 Next Hadith → the Messenger of Allah instituted the Ushr of what was watered by the heavens and steams, or through natural channels, and half of the Ushr for what is watered by irrigation.

Jami` at-Tirmidhi Book 7, Hadith 24