Hello, I would like to report my findings here. Trophy was earned on 17 June 2021
I had the same issues before, even when I had had all planks and planted at the same time. Reading some comments, I decided to go to a different island.
I went to a custom island as opposed to a generated one as the issue I was experiencing was on one such island.
As you can see above, you can view my previous arrangement and then my new arrangement when I arrived on the new island. (Take note that none of the plots are touching each other)
Items used:
Planks x 16 = 8 Plots
1x Ajuga
1x Aloe
1x Kura
1x Pipi
1x Potatoes
1x Quwawa
1x Wavulavula
1x Yucca
I did not need to water the plots to full as the trophy unlocked a few seconds after planting the last plant.
So maybe this can help. I would suggest saving the game before undertaking this task incase it doesn’t work so you can try again on another island.