Takenoko growing bamboo when gardner lands on non-irrigated plot
If you look at the faq on board game geek is specifies that the gardener will grow bamboo on adjacent plots if they are irrigated regardless of the plot he landed being irrigated. What is important here is that the plot that is getting the bamboo growth is irrigated.
https://boardgamegeek.com/wiki/page/Takenoko_FAQ

If the plot the gardener is on is not irrigated, the bamboo will still grow on the adjacent plots of the same color if they are irrigated.