Shmittah, or letting the land lie fallow every seven years, extends to plant pots outdoors and exposed directly to the sun. We are forbidden to tend our fields during the seventh year. But what about hydroponic plants?
The fact that hydroponic produce grows in water and some nutritive substance, absolutely free of any soil, means that farmers can grow it during shmittah. Plants growing detached from the ground in no dirt at all do not fall under the rules of shmittah.
The Chazon Ish (1878–1953), who ruled strictly on shmittah observance, banned hydoponics. He argued that anything that enhances growth, even if not grown in the ground, was forbidden during shmittah. Rav Ovadia Yosef (1920–2013) disagreed and argued that enhancing growth should not be a consideration. For him, whether growth was similar to planting in a field was the only factor.