I read that I can now plant a seed in pot, but I really did not understood how to do it.
I placed the pot on the ground and selected a seed but cannot plant them. What do I miss?
There must not be a previous plant in the pot, if there is one you need to remove it. You also need to click slightly above the pot to plant the seeds, not directly onto the pot.
You can't plant seeds, they're for shooting with the blowpipe. Try the alchemy plant seeds and click just above the pot.