Orlah and hydroponically-grown blueberries

Answer

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" (Vayikra 19:23), it would seem that water media are not considered "land." On the other hand, Rabbi Yaakov Kanievsky (Kehilot Ya'akov) holds that the verse refers to the time of entering the Land. However, this mention of land does not exclude plants grown in media other than soil. For this reason, orlah would apply to any means of planting, even if not in soil.

The posekim discuss hydroponic cultivation during shemittah vis-à-vis the prohibition of planting and the blessing on vegetables. Rambam rules that soaking wheat in water on Shabbat violates the prohibition of zore'a (sowing), so it seems that water is equivalent to soil. The posekim also discuss hydroponics vis-à-vis terumot and ma'aserot.

Nechpah Bachesef (I, 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 the shemittah year. All hydroponic media have fertilizers added to the water; some of these mixtures could be considered "soil," and thus orlah would apply.

Rabbi Shaul Yisraeli (HaTorah VeHa'aretz I, 5749) 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 Hateluyot Ba'aretz II–III, p. 161), who states that orlah applies to such trees.