Veggie Container Garden and Potting Soil

I bought two different potting soils for my container veggies experiment.

One was from a feed store, the other from Walmart. I put two cherry tomatoes in one container with the feed store potting soil, and six jalapeno peppers into the other container with the feed store potting soil.

I put one yellow pepper (sweet) and one yellow summer squash into the container with the Walmart potting soil.

So far I've harvested about 12 jalapenos, and maybe 75-100 cherry tomatoes from the feed store potting soil containers. The plants look a bit sparse, but still produce.

The Walmart potting soil container hasn't even produced any flowers on the yellow pepper plant, and the small ugly squash plant, it does make squash flowers, but they never become squash. Both plants are very small.

I need to learn about adding extra fertilizer, or other amendments, but I've learned NOT to use Walmart potting soil.