I think this looks like Nitrogen deficiency in the soil. You need to add a Nitrogen fertilizer for dark green leaves. I use a Nitrogen fertilizer till the plants are big enough and have dark green leaves. After that you can switch to a low Nitrogen fertilizer.

Poor soil. Probably that soil has lots of wood chips.
I would scrape away as much soil from around those plans ( up to 2ft in diameter and add decent aged compost and fertilize lightly.

Can you please tell us what soil/mix you used?

It is the soil. Add manure, or or mushroom compost. Your soil is too woody.