By Xinhua special correspondent Jing Haipeng
ABOARD TIANGONG-2, Nov. 13 (Xinhua) -- Greetings to everyone. Today (Nov. 11) is my 24th day onboard Tiangong-2. I am Xinhua space correspondent Jing Haipeng.
I have heard that people are curious about the gardening tests we are doing up here, so let me tell you about how we are growing lettuces.
We did some routine gardening today. We tested the moisture and nutrient content in the culture substrates, and provided our plants with light and air.
We use a device to test if the plants need more or less moisture, a lower reading indicates that our lettuces need watering. We also inject air onto the roots of the lettuces, which helps them grow better.
We are like farmers in space, and we have to spend at least 10 minutes everyday tending to our lettuces.
The culture substrate we use is not like the soil on Earth, it is a specially-developed mineral material.
We began the gardening tests on our second day in Tiangong-2. First we had to install the cultivation device, which came in individual parts -- like Lego. We installed the completed device inside a white box.
Then we watered and sowed.
In the lead up to this mission, some of the seeds had been processed into little balls and put into individual unit cells. Lettuce seeds are smaller than sesame seeds, so they had to be covered in a special coating to form mung-bean size balls, which made it easier for us to handle them.
The balls were designed so that the seeds separate from the coating when they come into contact with water, however, we have found that the coating affects the sprouting process slightly.
Sowing seeds in space is also different from on Earth, where we sow the seeds first and then water them. As the culture units in space are a solid material we water first and sow the seeds into the soft base.
After this, we put a piece of plastic over the culture device, which works like a propagator and prevent water loss.
On the fifth day onboard the space lab, the seeds had sprouted. My brother Chen Dong and I were very excited and relayed the news to our ground team. We took a lot of pictures.
After the seeds sprouted, we took off the protective film and turned on the lights. We used red, blue and green light, with red as the strongest color.
We also had to thin out our seedlings on the sixth day after we had sown them. My brother Chen and I think the lettuces look very fresh and greener than those grown on Earth.
We used tweezers to pull out the weaker-looking sprouts and left two in each unit cell. We had to do this very carefully as the sprouts were still very delicate. Three days later, we did a second round of thinning and watering. This time, we only left one sprout in each cell.
We do not need to water the plants everyday. According to agricultural experts, we only need to water the plants five times. We use syringes to water the roots.
Also, we have to observe, take pictures and test the lettuces everyday.
The lettuces have been growing well so far, and we are satisfied with our work.
Some people have asked if the sprouts grow in a different direction in space. All our lettuces have grown upward, like on Earth, but it does seem that they are a bit taller.
Tuesday will be the last day we tend to our vegetables in-orbit. We will take samples from the plants -- leaf cuttings and sections of the roots, keep them in a low-temperature storage device and bring them back to Earth.
Another question has been whether the lettuces will be edible.
This time, these vegetables are just for experimental tests, and will not be eaten. However, I believe that after further research, space-grown vegetables will be edible. I see a future where astronauts eat the vegetables they have grown in space.
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