Check the pH of the runoff next time you water. That soil looks very heavy too.
What are you feeding them? They need a complete fertilizer. You might also want to add more drainage in the pots- that helps with soil chemistry.
Also, decomposing wood chips/sawdust are bad for potted plants. I can't remember where I read the explanation, but I seem to recall a mention that decomposing wood actually scavenges N from the surrounding soil. I can't remember, but either way it's not good for young plants in pots. Save the mulch for older, established garden plants with good root systems.