It means to grow plants without soil, in a liquid medium containing enough nutrients to maintain the plant.
Sure you can
corn is the easiest but pretty much anything
it is not poisonous to animals
the plants will grow because soil contains a lot of minerals
to produce something or to grow.
you are excited for something
I believe it is something a man will do to grow his penis.
There are two kinds. Some squash grows on a vine (like pumpkins). Other squash grow at the base of a single large plant (like zucchini).
bamboo will thrive in water...with no soil. Many plants grow hydroponically (in liquid), e.g. tomatoes, lettuce, etc. The procedure can be complicated, so you might want to consult a book about hydroponics at the library.
"Dwindle" means for something to gradually grow less or smaller
Unless this is something totally different that I haven't heard about, Hydro is just Cannabis (Marijuana or Weed), that is grown hydroponically instead of organically.
A hypothesis is a question that a scientist comes up with, which will later form the basis of experiments or testing which will attempt to answer the hypothesis. For an avocado, an interesting hypothesis might be, 'Will the pit of an avocado grow hydroponically?'