I am currently using Southern Ag 5-11-26 (very similar to Jacks or Peters). You can use the 321 formula start to finish, but a few things I’ve noticed:
- Could use an N bump in veg (can be improved by using mag nitrate instead of epsom as the “1” in 321)
- Could use a P bump in the first 1-2 weeks of flower (Jacks recommends 10-30-20, I am supplementing Fertilome 9-58-8 right now)
- Could use a K bump at the end of flower (Jacks recommends 7-15-30, I have been supplementing MKP)
Some strains will complain about 1 or more of these things in strict 321 start to finish. That’s why Jacks cannabis schedule uses mostly 321 interspersed with some of their other formulations like @Papalag is saying.