I agree, you will need a bigger pot. I use 7 gallon pots but that is actually small. Most organic growers are using 10 gallon or bigger. The bigger pots are better because the more dirt you have the more living critters you will have processing the nutrients to feed the plant.
I use the smaller ones because I have back problems and I’m allergic to pain. I do okay with them I just have to stay on top of my feeding schedule to keep the plants from getting hungry. I also try to keep my plants on the smaller side. Smaller plants eat less obviously
Ms @Caligurl is correct. Highway Dust is a dry organic nutrient mix. You put it on top or your dirt and lightly rake it into the top inch and keep it moist.
Check out Ms @Caligurl latest grow. Here’s a link. She grows in much bigger pots and has some gorgeous monsters growing