Since these grow naturally as weeds in the soil of my yard, I assumed they don't really need less acid soil nor extra fertilizer. That may be a problem. Maybe they would do better with fertilizer, but since they manage as "volunteers" I don't understand how what I'm doing is worse.
Most of the soil in my yard is decomposed pine needles and oak leaves. I selected soil with more long ago decomposed material and less of each of last year's pine needles, clay and sand.
Before and after they sprouted in Aug, I kept the trays outside all the time and moved them during the day to get more full sun than any spot in my yard gets and watered twice a day to keep them consistently moist but not drowned. As it got cooler I switched to bringing the trays in at night, then out during the day (during that long period only the cotyledons were visible).
Once it was getting below 32 outside during the day, I moved them to south facing windows in a cool room, where the nighttime and cloudy day low temperatures dip just below 50 and the solar gain on a sunny day gets them a bit above 70.
I'm watering every second or third day, now that there are significant roots to pull from below the surface. The soil surface gets dry in 3 days, but below the surface stays moist. There are openings at the side on level with the bottom of the dirt and I never water enough to get water to flow out of those, but just less than that.
Even with extreme care, adding water on top of the dry surface, it beads and runs around the surface for a while before soaking in. That momentarily puts the tiny plants under water, which I don't think matters. But it also washed dirt on top of the cotyledons of most of the plants, which stuck, so those plants have only the two leaves that followed the cotyledons visible. Even in five months, I don't think any of the cotyledons simply died off as you suggested. Most got buried. The rest never changed.
You implied true leaves continue to grow. I'm pretty sure they haven't. On each plant, each leaf has reached it final size before the next leaf started. Those final sizes vary. But each seems to definitely stop growing and the next leaf doesn't start until it has stopped.
In the photo, you see a leaf that was starting for a long time (after the large one before it stopped). Relative to the otherwise glacial pace of this plant, it then took off and in 9 days since the photo is almost as big as the smaller of two before it. I assume it will continue and be largest before it stops and the next starts.
I will be away the first week of April and won't have anyone to water them. Obviously the volunteers survive a week without rain frequently. I hope these are that strong by April. Maybe I need to move them to bigger pots in early March.
All these were from seeds from the white flowered campanula. All the volunteers except one were blue flowered. That one had two flower stalks when I found it, which I divided on transplant to two plants. Each flowered multiple times and then formed a large rosette still green through the severe weather. So I think I have two healthy white ones. But I prefer for nearly half the plants to be white. I expect all the volunteers I find and transplant in the spring will be blue. So these seedling may be required to get more white flowered plants (if they breed true, which is questionable)
