Of course, digging up the mountain beans was just one of the reasons. Another reason was that Zhao Hai wanted the children to get closer to nature so that they could get to know the plants he had talked about the other day.
A botanist was not a profession that always kept to one's book. One had to be close to nature, not only because it would speed up one's cultivation, but it would also allow one to understand plants better. If a botanist could not understand plants, then he was not a good botanist at all. If one often communicated with plants, it would slowly become easier for one to communicate with plants. Therefore, besides digging up the yam beans, Zhao Hai also wanted the children to communicate with plants properly.
