Semps are usually trouble free, and there is not too much to look at here with your problem. Didyou transplant them before the third leaf appeared? Generally they can survive that, though. I would guess the soil is a bit over wet and the roots can't handle it, or they may be too close to the lights and the heat is building up someway.All my seeds grow about a foot below a two bulb 40w fixture, whether they are semps or species.

Thanks woebegonia for taking time to post! I'd like to think I've done a good job of monitoring media moisture, however there is that chance my lights are too close (3" above flats)...... Media temps stay around 60-65F & my petunias (under the same 4bulb-32W/4' fixture) seem to be fine..... I hear lots about lights not being close enough, but perhaps I'm over the top.... I have one more flat about to come off heat & I'll raise the lights over them to see if it helps.....

Transplanting isn't an issue due to the fact I haven't made it that far yet..... LOL I see pics of folks starting begonias in peat pellets (ugh) & they've done great...... Makes me think I'm trying too hard.... :(

i think medium at 60-65f is too low for begonias. search 'begonia from seeds' even on this forum. 70's is what other people keep the seedlings at.

i think medium at 60-65f is too low for begonias. search 'begonia from seeds' even on this forum. 70's is what other people keep the seedlings at.

Valid point. My temps might be at least part of the problem. Pro Mix tends to hold lots of moisture..........

Raising temps poses a problem because I do my propagating in my 30x40 shop.. Although heated, it struggles to maintain heat with the brutal winter we're experiencing here in Kansas......

I wonder if you have damping off disease.