I started my tomato seeds about a month ago. Most seem to be doing okay, though I notice that a fair number have grown to about 1.5 - 2" tall and then they stop branching (if that makes sense) and they stop growing taller. I've composted about 10 that have done this.

Does anyone know what causes this?

Is this indoors in pots, or outside?

And what is the weather like, or indoor temperature? Whichever applies.

Are you growing in a sterile seed mix? Can you post pictures?

Is there any yellowing of the leaves?

I would suspect that something is wrong with the seed-starting mix, as it pertains to tomatoes. It may have too many wood chips in it, or something like that.

Potting soil with partly composted wood chips can be all right for houseplants long-term, if you fertilize regularly with a fertilizer that contains nitrogen, at first (it can slow growth in the short-term, though), but for starting tomatoes, it's not great, because the plants don't get enough nitrogen, and giving them enough in that situation can be tricky without burning them.

Another possibility is that the soil is too salty, or possibly that it has residual herbicide in it.

Anyway, those are just some ideas. I don't know.

too wet too cold amount of light per day soil no fertilizer
I had seeds that popped when I was away from home and they "bolted"
I have the light very close now but they are still the same but still alive.
I don't have a worried look upon my face.
I may just add more soil around them.
They are still at the cotyledon stage.

Even using full strength MG on seedlings I haven't had burn problems.
Normally about a half shot.

Thank you all for your replies!

@Rockoe10 The tomatoes are indoors, in a small room that bumps out from the main part of the house and has large windows on three sides. The room is cooler than the rest of the house (it's poorly insulated) but it gets a lot of sun.

I don't have any left of the stunted/non-branching transplants, as I composted them. If it happens to any more, I will post pictures, though.

@Shule - I hadn't thought about the matter of woodships in the soil. That's a good point. I've used a commercial brand for years without problems, but did find myself surprised at the amount of wood chunks/chips in it this year. I will try another kind and see if it improves the situation for the next batch of tomatoes I plant.

@PlainJane - the potting soil I've been using is called "Golfgreen". The bag says it is a blend of soil, peat moss, and Perlite. I don't think this is a sterile potting mix. (Would it say on the bag if it was?)

The transplants might have gotten too cool/wet. Things were going along fine until the temps dipped and we had overcast weather for a week. I've got as many transplants as I can have on heat mats, and the rest are just under grow lights.