Here's one of my seedlings planted in the 3rd week of September.
You'll never guess what made it grow like this. In this photo, it is
12 inches tall, and I have trimmed the tops numerous times.
No artificial lighting, just a south-facing window, well, actually it is
double doors, so floor to ceiling. There are 97 pots like this with an
average of 5 seeds to a pot.
We will begin to acclimate mid April for two weeks, and plant outside
near the end of April or early May weather permitting.
The answer: After an application of liquid fertilizer that did nothing to help
the seedlings grow past their pale green 3 inches, hubby suggested we try granular 10-10-10.
He added a pinch carefully avoiding contact with the seedlings, in case it might burn
them.
It worked. The seedlings have been fertilized only twice all winter, and need no
further feeding.
On edit: The yellow coloration on the foliage is a reflection of the incandescent lighting
above. Nothing wrong with the plants.