I've used only natural fertilizers and amendments for 30+ years, with great results. For fig babies, I use fish emulsion, though the odor isn't good if your figs are inside. I add ground oyster shell, compost, and rock phosphate to potting soil when they go into pots. During the season I fertilize with fish meal, and or cottonseed meal, which is slightly acidic. I also top dress with more compost, which I make with horse manure and wastes from my garden. I've used the ground rock phosphate for many years, as an alternative to bone meal. It is supposed to break down slowly, releasing phosphorus for 3-4 years. Though new to growing figs, these things in one combination or another, always yield great results, as they feed the soil.