We had a lecture about this at our bonsai club. One of our members explained in detail what to use, which NPK levels to use in which season, the difference between solid and liquid fertilizer, the effect of temperature, how to apply fertilizer, when to remove (solid) fertilizer that was no longer effective (as the nutrients flushed out), when and when not to fertilize.
One of the older members wanted to add something after the excellent presentation. He showed how he ground up sphagnum moss, mixed it with fertilizer and put it in (Japanese) tea bags, that he put on the soil. Note that he is a known person in the bonsai world, a pioneer that already did bonsai before it became popular, has visited Japan numerous times, has loads of knowledge and awesome trees. His reply to the question when he removed the bags was:
Never.