Biochar is a type of charcoal that is used in soil amendment. Going through each of the given options:

Option 1 states that Biochar can be used as part of the growing medium in vertical farming. This is correct because biochar is often used in agriculture, including vertical farming, to increase soil fertility and agricultural productivity.

Option 2 states that when biochar is part of the growing medium, it promotes the growth of nitrogen-fixing microorganisms. This is also true. Research has shown that biochar can enhance the presence and functionality of these microorganisms which are key in converting atmospheric nitrogen into a form plants can use.

Option 3 states that when biochar is a part of the growing medium, it enables the growing medium to retain water for a longer time. This is also correct; the porous nature of biochar allows it to hold onto water and retain it for an extended period, moderating water stress in plants.

Therefore, all statements (1, 2, and 3) are correct, making option 4 (1, 2 and 3) the correct answer.