The active ingredient in Superthrive is naphthalene acetic acid, a synthetic (auxin) rooting hormone. It is effective, but there are a couple of
caveats. The first is that you must get a freshly-manufactured batch, as the synthetic hormones are chemically unstable, so degrade relatively quickly, rendering it unaffective. How you determine the age is beyond me, as they don’t put expiration dates on the packages. Dyna-Gro KLN is a similar product containing two synthetic hormones, but they are smart enough to specify the expiration.
Be careful not to overdose them. Excessive hormones can result in deformed flowers or stunted growth. With extreme dosing, they can kill the plants.
A really effective root-growth stimulant is Mega Thrive. It is a urea-based foliar fertilizer containing “mega” doses of boron and molybdenum. That extreme dosing of those trace elements stimulates the plant into producing auxins which stimulate root growth. Like the synthetic hormones, those same overdosing issues exist, but on two layers - one is the effects of excessive auxins, the other is that large trace element doses can kill a plant. The one thing that prevents me from using it is the toxicity of the molybdenum, and the fact that treated plants are immediately toxic to birds and mammals, so any chewing critters, like cats, puppies, and grandkids, are in danger.
The Kelpak “Dusty” mentioned is a unique kelp extract out of South Africa. It is loaded with all sorts of beneficial phytochemicals that, when administered, act sort-of like a “plant IV”, to boost the plant in many ways, including root growth.
It is perfectly safe to use, and has a long shelf life. You can search here for more info, but these are tickets might be of interest:
growth stimulants
comparing seaweed extracts
Kelpak