In addition to the NAA and vitamin B1 - both root growth stimulants - there are a wide variety of other organic and inorganic "goodies" in it, such as humates and kelp extracts. Personally, I think the rooting chems are the most significant part.
Many years ago, seeing the price of the stuff, I decided to make my own version. I did a bunch of research on the effects of various vitamins and chemicals on plant growth, then mixed up my own concoction from retail ingredients. Even at that, mine cost less than 15% of the cost of ST,
I DID run a more-or-less controlled comparison using 50 seedlings each of Phalaenopsis Lemforde Novelty and Oncidium Sharry Baby for each section - all were fertilized, but one group got nothing else, one got 2 drops per gallon ST, the third group got my stuff added at the same rate - a total of 300 plants.
There is no doubt that after 3 months the plants receiving the supplements grew faster than those that did not, and it appeared that my stuff actually was better than ST, but it was probably not a statistically significant difference. I probably should have continued the experiment longer to confirm or deny that.
Instead, I embarked on trying to see the extent of treatment, so I took the two additives, and increased the dosing to a teaspoon per gallon on some of the phals - I sold the rest and the oncids to regain bench space. The plants continued to grow well, but when they bloomed, all of the phal flowers were crippled. The oncids were still to small to bloom, and after stopping the overdosing, the phals resumed blooming normally next season.
I have continued to play with SuperThrive and K-L-N (NAA, IBA, and B1) over the years, and have concluded that if there is something "iffy" about your culture, they can help, but if you're doing a pretty good job with your plants in the first place, they add little, if anything. I only use them as a soak for transplants - sort of a "kick start" to help them get reestablished.
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