10 days into seeding and with little to show. Initially suspected that the seeds quality have dropped due to prolonged storage or caused by the washed leca, that may have absorbed residues of bleach. Another possible reason is the increased evaporation. A closer inspection showed that those which managed to germinate, the cotyledons broke off from the root. Hint of rotting... So suggesting that the leca was not cleaned well. Decided to reseed another batch of seeds in an upcycled greenhouse, made from a Butterhead salad packaging. Used fresh leca, and seeded 2 days ago. The result... And close up... All the hair roots can be seen clearly. What a difference! All 4 types of seeds (BH, RO, GR, L21) germinated well. So it's likely a more optimum environment due to the new clean leca and the greenhouse condition which reduced evaporation and kept the seeds moist enough to germinate. Key takeaway #1, leca or grow mediums needs to be cleaned thoroug