The gemara says that we only make "ha'adomo" on something that grows and receives nourishment from the ground, to the exclusion of mushrooms which are considered to receive nourishment from the air not from the ground (When i said this over, a microbiologist took some offense to the claim that mushrooms receives nutrition from the air more that any other plant. I responded that perhaps nourishment from the air is simply a way to refer to the fact that they can be grown on moist logs and things of that sort that are not at all connected to the ground. Air may simply be a way of saying not the ground). The question is raised regarding what bracha to make on vegies grown in water - hydroponics. The Chayei Adam (51:17) writes that wheat grown in a flower pot would not be subject to "hamotzi lechem min ha'aretz" since it would not qualify as "aretz". Similarly, he proves from a gemara in Chulin 139b in the context of shiluach hakan where the gemara says that a nest on a persons head would qualify for the mitzvah, since a person is called "adama" and therefore dirt on a persons head retains status of "adama", whcih he the gemara proves from a pasuk. From this he deduces that if the connection is broken with the ground it will no longer qualify as "adama", so a borei pri ha'adama can't be made (this would seem consistent with the nishmas adam posted yesterday that brachos follow loshon hatorah, because otherwise he could not prove from a pasuk that it is ha'adama for brachos).
Although even if one were to argue with the Chayei Adam regarding vegies grown in pots, that could be based on the fact that dirt is called "adama" even inside a flower pot and therefore the bracha of "ha'adama" applies. But, water would certainly not qualify as "adama" and therefore one cannot make "ha'adama" on vegies grown in water.
The argument can still be made that vegies which are normally grown in the ground and the fact that the seed originated from the ground, ha'adama should be made even when this particular cucumber is grown on water.
See the Nishmas Adam (152:1) where he discusses a lulav grown in a pot whether it qualifies as an "eitz". His conclusion is basically that regarding bracha it would qualify as "eitz" and therefore one can make "boreh pri ha'eitz" on a fruit grown in a pot. Someone in my daf shiur pointed out that if this is true then we find an example of a situation where the bracha of "borei pri ha'adama" will not work even beidieved for something that requires "borei pri ha'eitz".