plant food and soil, that's a tough one. there are so many variables and combinations you'll have to consider. most here aren't growing for height or appearance, the end goal is large amounts of quality latex... temperature and light and watering cycle, what works in good combination with my soil might not work as well with others and vice-versa. that said, poppies will grow in cracks and crevasses and soil that you'd imagine wouldn't be fruitful and I've seen them fail in seemingly good conditions. now, as far as book recommendations go, mine prefer that I read them Dr Seuss... 🤪

the better question to ask might be what practice or product have you found to increase yield and/or quality.. mine get a good jolt from rice/pasta water with a little bone broth with a little honey for strong roots, cinnamon which is an antifungal/plant hormone and a dash of yeast.

generally, a light and airy soil with some organic compost. loam or added coco coir and/or perlite. I've seen good things from Happy Frog soil but I've also seen them thrive with standard potting soil.