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Why? What's wrong with B vitamins or why do you think they are useless?
Application of vitamin B-1 (thiamine) to root systems of whole plants does not stimulate root growth. This myth arose from early work on plant growth regulators, called auxins, which were mixed with vitamin B-1. Further research throughout the last half of the 20th century investigating the application of auxins to root systems suggested that auxins may stimulate root growth, but that vitamin B-1 on its own does not. Delving deeper into manufacturer claims, many rely on early research (late 1930s and early 1940s) which has been refuted by subsequent research and/or research done on plant roots excised from the mother plant or grown in artificial media (without soil).
Various studies using both woody plants and annual flowers and crops failed to demonstrate that vitamin B1 treatments provide any subsequent growth response. Conversely, vitamin B-1 (thiamine) is an important component of tissue culture media where plant tissues are propagated using sterile conditions and artificial growth media. “Miracle growth” claims used by companies selling vitamin B-1 are usually taken from tissue culture research. Healthy plants manufacture their own vitamin B-1 making it unnecessary to add any additional amounts. Many fungi and bacteria associated with plant roots also produce vitamin B-1, so it’s likely that healthy soils will contain adequate levels of this vitamin without amendment.
https://cals.arizona.edu/yavapai/anr/hort/byg/archive/vitaminb1androotstimulators.html