MrStinkyanswered grow question 3 years ago I would say use biobizz - you are in the ground so feed the soil not the plant.
Suggestions: epsom salts for a watering, guano with a high P - go gentle with it, or grab some biobizz, maybe fishmix, bloom and some topmax or something.
Synthetics can kill microbial life and because you in the ground that is a bad idea.