I have 2 houses, a 16x18 and an 18x18 that I am using for planting. And I have sorted all the seeds by which creature I got them from. Hopefully, with at least 20 from each creature, I'll be able to sort out all the groups and which each monster drops. I planted them all in fertile dirt.
Hopefully, I don't ruin this, but I do want to share. Currently, you can get the seeds from champ spawns. Example, the Toko champ has Kappa's and Hiryu's (well, honestly, my wife and I couldn't level it up to Hiryu's with just us two, we got to revanant lions/lessers but couldn't get past that), and the spawn inside the twisted wield for Dryads (not sure if the shadow wisp drop the seeds, I didn't check and already had 50 from them). Also, there is a lake where both Kappa's and Tsuki Wolves spawn.
Anyway, just wanted to share.