My initial reaction is overwatering. The 'healthy' one looks slightly wilted to me too, I'm afraid. Also the plants seem a little etiolated ie not enough light and too much warmth prompting soft, sappy, elongated growth. I think the best thing would be to try to dry them out ie don't water for a good while and to try to toughen them up a bit by lowering the temperature they are in. Also If a plant wilts there is no reason to cut off the wilted parts unless they are clearly diseased. If it is lack of water they will perk back up. If it is too much water they may still revive eventually. Is it warm enough where you are to put them outside in the day time for a few hours?

i dont have time.. nor patience [actually its a harecore coffee buzz.. lol] to do this flowery.. dont read in any 'tone' ..

the greatest conundrum in growing things in pots in the house..

you see wilt.. so you water it..

i have killed many a plant this way..

wilt means the roots arent processing water.. you default to more water.. been there.. done that ...

you have rotted the roots off.. as i have many a time..

you need:

better potting media..

you need to let them near dry.. and see if they have enough un-rotted roots to survive...

and should sterilize your media before you use it... the pathogen may have come in the media ...

and you have to learn to let things near dry ... in between drenching ...

ten more years of practice.. and you should be all set ... dont give up ...

and i do hope some survive ....

ken

Here is a link that might be useful: i use the micorwave ... if i have 4 pots.. i use 5 pot fulls.. dampen.. and heat

Well okay then lol. I put them outside today, I will be slowly hardening them off and keeping them out weather permitting until transplant time. I may pot them up. I don't think the roots are rotted, all of the other plants are fine...and every other plant I have used the same potting mix is doing fine as well, don't think there is a pathogen that caused the problem. Thank you for the feedback!!

super.. i wish you luck

if nothing else.. and not having seen nor held the pot.. all i can do is give you variables.. wild speculation at best..

and then you contemplate the variables.. and go from there..

but ... i suspect .... water management.. is at the root of it all.. [good luck

ken

I plant to get my newly constructed cold frame out in the garden this weekend, but not to put any tender plants/tropicals in it until at least around April 10-15 (three weeks or so before the average last frost).

I suspect it is way too early to put dahlias outdoors in Utah.

Yes I put them out in their pots and bring them in at night. I won't be planting out for another month or more.