really dont look like much for 4 weeks your plants should be waaaay bigger, what lights you got on them?
Right now, they're under 4x 26w 6500k CFLs.
how often are you watering them? also are you adding nutes?
I water them when the top inch or so feels dry... probably every third day. When they were new, I was watering more, but smaller amounts of water... After 1-1.5 weeks, I found out this is the Wrong Way(tm), and cut that out.
I tried adding nutes at about 2.5 weeks, and it seemed they didn't like it a bit. I've stopped giving em nutes again.
I think you are over watering them.
The soil in the pics looks soaked and the yellow leaves is an indication of too much H2O.
Stick your finger in the soil at least an inch down and if it is dry then water. They do not need to be watered everyday, if you have a good soil then you can water them once a week and add nutrients every other week or every 3rd week.
Yeah, the soil is indeed soaked, I'd just watered them about two hours previous, after ~3 days of nonwatering.
My soil is Fox Farm Ocean Forest, mixed with coco coir.
I think I just stressed the plants too much, and now I've got damned bansai plants on my hands... I just started germing more beans- I hope these have better luck.