The greenhouse, first sent up in 2002, has been used for 20 plant growth experiments so far. Now, a second unit has been added, and the lettuce crop was the first experiment to test different conditions side by side.

For many years, the experiments have sought to confirm Earth side results which show that minimizing water usage and salt accumulation would lead to healthier crops. During this experiment, two different root growth mediums were used. One was the traditional root pack used on all the previous tests. The second was the new and improved root pack, with slow release fertilizer. The hypothesis was that the slow release would help reduce salt intake.

Science is sometimes best when things go wrong.

The results suggest that plants in space need a larger volume of water and a faster rate of fertilizer than they do under normal gravity. Shane Topham, an engineer with Space Dynamics Laboratory at Utah State University in Logan, said that “the conservative water level we have been using for all our previous experiments may be below optimal for plant growth in microgravity”.

Overall, the garden experiments have four objectives:

• Can the crops grown in space be consumed safely
• What microorganisms grow on the plants, and how do you prevent or minimize microorganisms in the modules prior to launch
• How do you clean and sanitize the crops after they are harvested
• What conditions optimize the production of crops in microgravity

One additional objective of the experiments is to measure the non-nutritional benefits (stress relief, etc.) that crew members experience working with plants in space. Growing and tending to the crops provides comfort and relaxation to the crew. On a long voyage, this activity may contribute to the success of the mission.