Why have my tomato seedlings collapsed?

[TonTonMacoute]

I germinated them on a heated mat, they looked good and strong so I put them in the front porch and they have just keeled over. Could it be too cold at night?

Its not damping off because they were not too damp and in cool airy conditions.

Have they gone leggy? How many leaves do they have?

Sometimes watering from the top rather than the bottom also leads to collapse of early seedlings - tomatoes seem to be especially susceptible.

not sure about temp - is your front porch enclosed? I wouldn’t put mine out yet, as it is still pretty cold many nights.

This- we are forecast around zero at night for the next week so even an unheated enclosed porch might be too cold for tender things like tomatoes. Min night temps of 10 is usually recommended.

Not leggy, just seed leaves so far. I'm very careful with watering so I kept their propagator covers on.

The porch is fully enclosed and south facing, but I haven't checked how cold it gets at night - and it's been very cold here this week so I think that's the most likely.

I'll start some more off and be a bit kinder to them!

Good plan, theres loads of time! I'm sowing mine at the weekend and I've done it first week of April plenty of times.