Q: I want to grow a blueberry bush in my house hydroponically, using water and fertilizer. The bush produces fruit by its second year. Does orlah apply to trees grown hydroponically?
A: This is a new question that is hardly mentioned in halachic responsa, since hydroponic tree cultivation is a novelty.
Since the verse discussing orlah states "When you come to the land" (Devarim 26:1), it would seems that water media are not considered "land." On the other hand, Rabbi Yaakov Kanievsky (Kehilot Yaakov Gitin 6) holds that the verse refers to the time of entering the Land, but doesn't exclude plants not grown in soil. For this reason, orlah would apply to any means of planting, even if not in soil.
The poskim discuss hydroponic cultivation during shemita in terms of the prohibition of planting and the beracha on vegetables. The Rambam (Hilchot Shabbat 8:2) writes soaking wheat in water on Shabbat violates the prohibition of zore'a (sowing), so it seems that water is equivalent to soil. The poskim also discuss hydroponics vis-à-vis terumot and ma'aserot.
The book Nechpa Bakesef (1, YD, 5) writes that if one puts a bit of soil in the water, it is forbidden to use the mixture as a medium during shemita. All hydroponic media have fertilizers added to the water; certain mixtures could be considered "soil," and thus orlah would apply.
Rabbi Shaul Yisraeli (Hatorah VeHa'aretz 1, 5759) deliberates whether orlah applies to unperforated pots; while inclined to exempt hydroponically grown trees, he writes that he nevertheless did not rule this way in practice.
The only posek I found who writes explicitly about orlah and hydroponics is Chief Rabbi Yitzchak Yosef (Yalkut Yosef, mitzvot hateluyut ba'aretz, vol. 2-3 p. 161), who states that orlah applies to such trees.
In practice: the rabbis of the Torah VeHa'aretz Institute rule that orlah applies to hydroponically grown trees.
