Seedlings stay tiny and will not grow

Hello, it's difficult to say. Could be low nutrient levels, root issues, light, heat, watering. If I had to guess though, it looks MOSTLY like a light issue (not enough). Personally I'd probably transplant those into a "hotter" soil mix (a bit more nutrients) and give it more light. Best of luck.

Plants need at least 6 hours of DIRECT sunlight to grow properly. Glass also stops UV light, which could be another factor in their slow/small growth. Cheers, Organoman.

Lack of light for sure if it is just on a window ledge.

They probably just need some time to develope their rootsystem - be patient - as you say - they look healthy. 😎 How hot is it in your windowsill? Your pots are black and absorb heat very efficently. Little seedlings ar best of when its kind of cool around the roots.

It will be lack of light most probably my friend they look really healthy nice shade of green not dark or light in any spots really mean yeah I would assume its just the lack of light from the window. My top guess anyway pal If you wanna keep going just put a wooden kebab skewer in there to help support her and you will be fine :)