On Siren too. I reckon its:

1) 14 day trial
2) host mule gives 10 pots/20 wildgrass seeds to trial mules
3) mules NPC them in 14 days and give pots back to host mules
4) start another trial

No way I can see to get around it without destroying the wildgrass seed result npc price unless they can implement a nerf on gardening similar to the nerf on fishing and not let trial accounts garden.