Thank you Adriann, I hadn't come across the Chinese floating gardens before - I guess people all over the world can come up with similar solutions to similar problems, which is one reason the internet is so awesome - giving us this information in our homes and screens. Do you know if there are any European examples? I think Europeans have a habit of draining swamps rather than using them as they are....
I didn't find any English language information but thanks to google translate this site from Hongkong:
frame field edit
In the swamp, wooden stakes are used as a frame, water plants such as wild rice root are selected and mixed with soil, spread on the frame, and rice is planted, which is called Jiatian, also known as Fentian . The crops planted in this way float on the surface of the water and rise and fall with the water without being submerged. In the Song and Yuan Dynasties, there were such fields in Jiangnan, Huaidong, and Guangdong and Guangxi.
source
image here
( I couldn't link to the image - they look similar to the Bangladshi islands but appear to be covered in golden flowers)