They may need some food. They can only grow to about that size with the energy available from the seed so if you haven't put any fert on them they will stop growing in a sterile mix.

Or they may be putting most of their energy into growing roots at this stage?

After a month they should be much bigger. Something is holding them back. Most likely it's the soil. I planted mine on the same date and they are on their third set of leaves.

My guess might be the cups are to big for them and the roots are not establishing.

Too cold, too big of a cup for tiny seedling.

Ok thanks everybody, should I transplant them back in a smaller container and give them more fertilizer ?

Ok thanks everybody, should I transplant them back in a smaller container and give them more fertilizer ?

Yes, back into much smaller containers - save the cups that size for after they have a couple sets of true leaves - and when you do all that bare stretched stem needs to be buried. Cups that size with all that soil retains far too much water for such small seedlings.

But do not feed them until they have adjusted to the transplanting. Give them a few days to recover first.

Dave

Purple stems may mean they are a little cool.

I would add a shot of Miracle Grow at about 10% the recommended dilution.

Ok thanks Dave :) .. I only have Fish Fertilizer 2-4-1 from Neptune's Harvest, will that do ?

That's ok even tho it is organic. Organic liquids can work in containers even without the soil food web most require to be effective. Dilute it to 1/2 strength.

Dave

Could be a matter of warmth when they were planted. Tomatoes germinate best above 70 but grow as seedlings best at 60-something. So I germinate mine upstairs and bring them to the plant stand in the 60ish basement after that.

But I disagree about size of planting area. Plants don't know how much soil they are in. The only thing a small container does is cause the roots to circle and that's never a good thing.