I have had a lot of success in accelerating growth rates by focusing soil composition, and root health. I use a 3 part soil with equal portions of peat, topsoil and pine fines. I apply mycorrhizae to ensure root health in addition to humic and fulvic acids. Nutrient availability and the plant's ability to take in nutrients is easy to overlook, and makes a big difference. I also use espoma holly tone or tomato tone, occasional b vitamins, enzymes, silica, glacial rock dust. Probably missing a few, but the mycorrhizae is probably the biggest game changer IMO.
Best of luck!