Whenever you plant hemp it will consume all your hemp seeds in doing so also having the seeds wielded when planting will crash the game.
Seems planting was only implemented halfway through. Fixing this+more now…
Thanks for reporting!
Edit: it is done!
Thanks a lot 
Anyone with any idea on how long it takes for plants to grow? It has been around 20 game days and there has been no development on the seeds I planted. Do they germinate and grow slowly or do they spawn as an adult plant after a certain time period?
It’s 1.5 seasons IIRC, though you can fertilize them once to make them grow faster.