I will give it a shot, but not actually being there in person, I really can't say 100%.

I'm not sure what the trailing plant is from the picture, but based the look of the leaves on the one that is still has a little life, as well as the algae growth on the pot on the right, I think their is a drainage problem.

At the same time, from the image of the right pot, the soil looks dry.

First thing to do it to remove the trailing plants from both pots. This means all the soil under them. No matter the reason they are dying those both need to be removed. I would then start digging around in the soil some. What does it feel like. It is really wet? If so, when was the last time you watered them. Did the dying start after that? Did you add anything new? A fertilizer, mulch? Is the potting mix new or reused from previous years.

The other plants do not look horrible, but they do not appear to be thriving. The mix does appear to have a lot of bark. There is the chance the potting mix is too acidic. Did the bag say it is a potting mix, appropriate for annuals?

If the soil is wet, put some pot toes under the pots. This will lift them off the ground. There really is not much space between the bottom of the pot and the floor for the water to run out. It will also help protect you concrete (or whatever) from getting stained. And hold off on watering.

You can test the soil's PH. Just buy a cheap tester. It will be acidic, but if it's really a low number you can add just a little dolomite. Just a little, scratched into the surface. Do the research, but I think it will be something like a tablespoon at most.

If any of this works, buy some new replacement plants. If it is a watering/drainage problem, try to remove any of the soil those dying roots were touching.

YOu can also add some Mykes, when you plant the replacements. It will help make your roots stronger and healthier.

thank you! sorry for the delayed response.