Spindly Onion Seeds
Onion seeds are about the only seed sthat we don’t grow here in Stephanie's Kitchen Garden - they are sometimes tricky to grow and I prefer to buythe organic sets. Besides there is always a lot going on in our greenhouse that time of the year and I can’t give them the space.
I’m wondering if you are keeping your seedlings too warm and maybe not giving them enough light? I’m not sure of the growing conditions you have grown your seeds in so it is difficult to say. When sowing seeds in our greenhouse we use Heat mats to aid germination and then remove them from the heat and put them under Growlights to give them plenty of light. The fact that you said your seedlings are spindly is common with onions and leeks as they thicken out later but maybe lack of light has made them more spindly than usual.
Onion seeds often fall over, try giving them a little bit more water in case they are not getting enough water to support themselves. I would give them more light and water and get them a bit stronger with a view to hardening off before planting out.
I hope this helps and that your seedlings pick up soon.