I say, and with God's success: If something that is not beneficial grows in the land, such as grass, firewood, reeds, and others, then zakat is not obligatory on it; because the lands are not cultivated with these things. If he makes his land a place for firewood, reeds, or grass, then zakat becomes obligatory; due to the existence of cultivation. As mentioned in the explanation of Al-Waqayah, p. 67/A, and God knows best.