That's a good point tsud.....air is just as important to roots as water.

try adding 1tbsp of epsom salts to one gallon of water that will green up the plant

Back off on the water. Stick your index finger in the dirt (no meter)about 3 inches down.. see if its dry first. The roots s/b only about 5" to 6 " deep at this point.

Agree finger in the soil is the best way to tell if plant needs water.

I suspect the soil. I get a feeling it's potting mix. I get the feeling that the beans reached for something with their roots that they didn't like.

I think you need to reach into the soil and see and feel and smell whatever might be happening. Go down as deep as you need to.

How deep are those beds? They look like maybe 8" If they are less than 24" off the ground it could be a problem. They may have hit bottom. What is the bottom material? Does it drain? Just asking to get to the root of the problem.

I think if the beans had been planted in your soil, where the grass is growing, they would be looking healthier.

Sometimes we try too hard, and make life hard for our plants.

Your planter boxes are really lovely and I would be proud to have such in my garden. You could experiment and turf out all that mix that you have in there, and put in some soil from your own yard. I really think you would grow some amazing vegetables.