What will happen if orchids grow in soil or drift wood?

They will grow in both, and they will just grow and probagate, most Orchids are "Epiphytes", they attach themselves to plants but generally to trees, they are not parasites they just use the plant or trees for support.

Other Orchids are "Lithophytes, they grow on rocks, stones etc.

There are some that are called "True Terrestrials", they grow in soil as opposed to the "Simiterrestrials" which grow on the ground on decomposing matter.

Please see related link below.