Unfortunately, the little ones had to go through a lot. It seemed like a potassium deficiency, which I tried to compensate with a GreenHouse BioGrow. This seems to have worked, but the plants have already suffered severe damage. It now seems like they are growing normally again.
Yesterday they moved to a 1.2m x 1.2m area under a 50W sanlight + initially 172W white/blue spectrum.
Thus the flowering began.
I also topped the plants 3 weeks ago, except for the smallest one.