Long-term space missions would need plants for recycling carbon dioxide and oxygen and producing food. However, growing plants in space is a tricky business – some of the basic signs of over- or under-watering (wilting and flopping) are simply not present in microgravity, and water does not spread through the soil as it would on Earth. Mary Musgrave of the University of Connecticut spells out some of the difficulties in a paper in CAB Reviews.
Microgravity also affects pollination, and the direction of airflow is critical for some species. Similarly, the debris from plants as they go through their normal life-cycle has the potential to block up ventilation systems. Harvesting seeds is also problematic.
The research area on space stations for growing plants have typically been very small (960 cm2), and none have yet been grown for consumption, and so there is much still to learn. Musgrave points out the flavour of plants will be affected by microgravity too. Small plants adapted to low light intensity and high carbon dioxide are being developed which would be appropriate for space travel.
The paper "Growing plants in space" by M.E. Musgrave appears in CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2007, 2, No. 065, 9 pp.