It looks like you have a good understanding on the topic, but a rabbinic rather then an academic. Let me explain you some points.
Essentially, what is hydroponics? and how can we grow vegetables that need soil without soil?
We study first what the vegetable needs and how it is receiving it from the soil, and we copy-paste it when we are growing them hydroponically.
The vegetable need sunlight, which is provided through artificial lighting. So forth it needs nutrients like minerals that it abundantly found in soil, but - you should know - that sometimes we need to add a certain mineral that is not found in the soil , in that area where we are growing, so we're adding it either. So when we grow hydroponically we can put the exact amount of minerals that the plant needs.
And with water, you probably understand that in hydroponics we have plenty of water.
So why is soil needed for?
The answer is, that it uses as a sponge, since the plant doesn't need too much water and we need to slow down the access water, so that the plant should be able to take up only as much that it needs.
So how are we doing it by hydroponics? In here we use a medium called "peat moss" with is composed of compost which is naturally found in nature. And which, fits pretty much the criteria of עפר הראוי להצמיח.
Although I'm not a פוסק, I hope that my words can grant some clarification, and of course you shall consult a qualified פוסק if you wish to use this product for מרור.
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