Never worked for me either. Hard mode on starting island. Tried first with wood plots planted each as I got them from other islands. After it didn’t work I cleared them all and replanted. Didn’t work. Then tried using plank plots … planted one after another as shown in image. Still haven’t worked.
Wait for Them to grow I guess
You cannot be on your starter island… Easy fix… go to neighboring island and try there. It worked for me no problem 
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Hi Noktavontavius, Welcome to the forums.
I’m sorry to hear this issue has occured for you in your save. We have a known issues report on it here: [Known Issue] "Who Needs the Sea Anyway?" Trophy Unlocking Issues which contains some workarounds including the one Dank-a-licous mentioned about traveling to a new island and planting there one after another.
If you continue to have issues please post a new bug report with as many details as possible in the Console Bug Reports section. We ask players to avoid reviving older posts as sometimes there’s newer information available and it also prevents your report getting missed in a comments section 
Thank you!
I got this today, I destroyed all my plots with all 8 plants then rebuilt all 8 corrugated metal plots and replanted all fresh crops that I picked right before I destroyed all of them. On my home base with no trees left with no coconuts. The trophy popped right after I planted the last plant. All my plots were not close to touching each other also.
Hi Batman, welcome to the forums!
Thank you for posting your experience of this issue and what worked for you! I shall add it to our Known Issues post (linked in my last message above) as other players may also find this workaround helpful!