Actually, learning how to grow plants in a space craft is vitally important. If we are to travel outside our immediate area in space, humans will need to survive on space craft for long periods of time.

The kinds of questions we need to ask are these.
How will people breathe in space?
What will they eat?
How will they get enough water?

Scientists today are experimenting with ideas for food production for the future in space. The interdependence between plants and animals on Earth will also exist in space. Plants can serve very useful functions in space. People will need oxygen, food and water in order to live. As we breathe air, we breathe out carbon dioxide (which is toxic at high levels to humans). Carbon dioxide is necessary for plants to survive and plants produce oxygen as a byproduct of their growth.

This reciprocal process between plants and humans is vital to life on Earth and will be necessary for prolonged living in space. Plants are also the ultimate source of food. With further scientific studies and technology, perhaps plants will be grown and used as a main source of food, and will be a way of producing oxygen and getting rid of carbon dioxide in a space colony.