I'm not sure, but since you mentioned damp off, I always sprinkle a little sphagnum moss on top of soil after planting.

Probably rotting from that heavy potting mix with yard soil.

Josh

Agreed, all 3 of your ingredients consist of tiny particles that lodge very closely together, filling every bit of space in a pot. In a pot, much larger particles (that don't fit so closely together, so they have tiny air spaces between them,) can help ensure there is also oxygen. Roots need oxygen & moisture at the same time to function. (Applies to any potted plant, not just Coleus.)

50 is more chilly than Coleus would prefer, if it's possible to keep the room warmer. If not, let soil dry, not to the point where plants wilt, but try not to keep soil soggy when temps are so cool. In general, plants use moisture very slowly in cooler temps (but this is sometimes mitigated by heat sources that cause the air to be very dry.) Check first to make sure plants are (almost completely) dry before watering. Picking up pots can help gauge that. Still heavy = still moist.

During the shorter days (and much weaker rays) of winter at high latitudes, some direct sun can be necessary for these plants to do well, though your altitude may mitigate that to some degree. When the sun becomes more intense and there are more hours of it per day, Coleus goes back to being the shade plant.

Once established, Coleus make fine house plants. And, of course, they love to 'play' outside for summer! Worth trying again, IMVHO. Good vibes!

Thanks for the replies; I have a few questions. What does peat moss on top of the soil do? Can anyone recommend a potting mix cheaper to make than buying the commercial bagged mix? And is there a reason they all started to die at once? Is the rot contagious?