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I've got a number of onion seedlings planting again this year. You can see my set in one of th epics attached. I've had success with them over the past few years doing them this way.
This year I've noticed, more than usual, that the tops of the seedlings are wilting, or falling over. You can see this in one of my pics also. I'm wondering what is causing it? Years past, I have noticed it on 2 or 3 seedlings. This year I have noticed it on about 12-15 of them. It seems the lower portion is fine, but the top is falling over. To date I've just cut off the wilting portion.
What could be causing this? Lights too high, or too intense, or too much water, not enough water. The soil is not drying out.

I have to do bit thinning, as some of the pots have 2-3 plants in them. But even some of the pots with just 1 plant in them are wilting over.

Open to suggestions, ideas or previous experience this issue.

Thanks in advance.

I'm noticing that its happening during the 12 hours of light. When I go to check on them and shut down the lights, I notice the wilting. After only 4 hours of light early this morning I had 6 more wilt over. I shut them off for the remainder of the day and had another two wilt over this evening.

Is it possible that its too hot under the lights? I have the lights a good 8-10 inches above the tops of the plants.

I also cut them all back today. Shortened them.

If it means anything, I'm using LED grow lights this year on the Onions. In years past I used my Flour. Lights. Would this make a difference? Everyone keeps telling me that the LED lights give off less hear, but I'm thinking theres more heat there. It feels warm under the lights and above the plants.

I can switch them out for the flour lights again, but it just becomes such a waste of money on the LEDS. Roughly $250 each. I bought 3 small sets like these, and a large 2' x 4' 6 tube LED Light... ~ $350.

I bought the smaller ones to place in the greenhouse too see of simulating a longer day on the day long onions would help with there growth, vs. ones without it. I planned on turning them on once the days here in north eastern Canada stopped being 14 hours (Sometime around mid september).

Anyway I look forward to some responses from the veterans or anyone who experienced this before.

How are you watering them? Have you retried the “heft”test to see if they are lighter/drier than they should be?... or too wet/heavy?

I just read your reply.

After dinner this evening, I noticed the top of the soil had be turning a bit green, which means I would imagine equates to the soil being too wet.

So I did the following:
- thinned them to 2 plant per container. Just in case I lose one plant in a container in the next week or so, I'll have some redundancy. Some containers had up to 4 plants in them.
- I trimmed the plants down to about 3 inches. This is 3rd trimming I had to do on these plants. Some of them are growing upwards of 6-7 inch.
- I removed any plant trimmings on soil surface.
- I stirred the soil slightly on the surface and removed any noticeable green.
- I placed a rotating floor fan on them for the evening. Starting to notice the soil that I stirred I drying out a little.
- I asked my wife to watch the watering of the plants... as I think me and her may have inadvertently over watered them.

Hopefully I will notice some positive changes in them over the next few days.

Applestar... nice to hear from you again! We have been watering them from the top of the soil. I've been reading that I should be watering them from the bottom. These trays and containers can be watered that way. Maybe I should change the watering method here?

The Heft test? First time hearing it. lol.I'm guessing its simply handling the container to determine if it feels heavy based on the water content in the soil? If it is, then I unknowingly did it tonight... and quite few of them felt heavier than the others. A few of them were actually wet on the bottom a little.

The room they are in is a constant 23 Celsius (74 F). But above the lights is def warmer when the lights are turned on.

I am also not using a heat mat. I have one that would be ideal for these 3 trays but I'm not sure if its something I really need to do?

I've never had this issue in the past. My only changed variable is the LED Lights. I even use these same containers for onions.

I have grown onions for many years, but never in pots or containers. I get a bag of onion sets (small dry onions) and go out in the garden and poke them in the ground. They don't need to be deep, just deep enough to stay put. They grow into nice big bulbs. I also plant a row of seeds. The seeds come up and make loads of nice green onions. If let go full season they make some walnut sized bulbs. Oh, full sun and water once a week. Have fun!