"Do you see the roots of that plant in the earth?"
Translation:Ĉu vi vidas la radikojn de tiu planto en la tero?
Because it's in front of the noun, modifying it, so you need the demonstrative adjective tiu and not the demonstrative pronoun tio.
The simple rule of thumb is: use tiu before a noun and tio when it stands alone.
The more complicated version is:
tio always stands by itself. It refers to something relatively unspecified.
tiu picks out a specific noun out of a group of other nouns. For example, tiu libro means "that book (out of the set of all possible books)".
It can actually be used without a noun, but there is still a noun understood. In English, you can't leave out the noun completely in this sense.
So while in Esperanto, la ruĝa libro "the red book" can turn into la ruĝa when you know that you are talking about books, in English you use the dummy word "one" in such a case and say "the red one".
Similarly, if you are talking about books and want to specify a specific one (see, there that "one" is again), you say "that one" while Esperanto could simply use tiu.
So tiu can stand by itself as well.
tiu can also be short for tiu homo -- so just as kiu? can mean "who?" or "which one?" or "which ...?" (with a following noun), tiu can mean not only "that ..." (with a following noun) or "that one" but also "he, she, it, that person, that one".
Second rule of thumb: if you see tiu by itself, translate it with "that one" rather than simply "that".
And bottom line is: tio never goes together with a noun as in *tio libro.
Eblas ankaŭ, mi kredas "ĉu vi estas vidanta la radikojn de tiu planto en la tero?
Yes, if your intended meaning is "are you in the state of seeing the roots of the plant"... Tio sonas strange en la angla, kaj "estas vidanta" estas stranga en Esperanto.
In fact, no. Your sentence means "Do you exist while seeing the roots of those plants?".
I see the roots at that moment, do vi povas diri "mi estas vidante nun la radikojn...'