Vitamin B1 or Superthrive has no demonstrable benefits for plant growth or vigor. It's certainly not responsible for some profound overnight plant growth.
Superthrive was debunked 80 years ago.
Here's but a few citations:
A product that has attained Horticultural Urban Legend status is Vitamin B1. The historical account of Vitamin B1 and the public craze it caused was well told by Rasmussen(1999) and is briefly summarized here. In the 1930’sCaltech’s James Bonner discovered, that Thiamin (vitamin b1) was able to restore growth to pea root tips that had languished in tissue culture. It was concluded to be essential in plant growth media. Bonner later found that B1 had little growth promoting effects on most whole plants in hydroponic culture, but that some plants such as camellia, and cosmos showed dramatic growth increased to added B1 vitamins. Bonner latter discovered that thiamin production was associated with the foliage of growing plants. The hoax was on in 1939 when Better Homes and Gardens magazine ran an article that claimed thiamin would produce five inch rose buds, daffodils bigger than a salad plate and snapdragons six feet tall! In1940, Bonner entered into collaborative research with Merck pharmaceutical company to master the growth promoting effects of B1, account for the wide variability in his experimental results and develop a product that gave consistent good results. Bonner proved during this period that B1 was phloem mobile was made in leaves and transported downward in stems. Bonner’s experiments with Cosmos continued, but with varying results, so he sought cooperative research with University experiment stations around the country. Results were mixed, some showed growth promotion, most not. By 1940,other physiologists widely reported negative results. By1942 Bonner was debunking his own discoveries, stating that the effect only ever occurred in very few plants and that since thiamin was found in soil itself, field applications were unlikely to benefit plants. Bonner ultimately fully retracted his claims of efficacy by saying “It is now certain, however, that additions of vitamin B1 to intact growing plants have no significant or useful place in horticultural or agricultural practice”. The public craze and fanatical headlines about thiamin continued but Merck withdrew all interest and funding in the concept so as to distance itself from a product that does not work.
University of California research on vegetables failed to prove that B1 reduces transplant shock or stimulates root development. Researchers found "no discernible differences in color or vigor among treatments" when B1 and B1 plus iron, manganese, and zinc were used on peppers, pole beans, squash, sweet corn, tomatoes, and watermelons. Elsewhere, studies on chrysanthemums, citrus, and roses have reached similar conclusions."
