In general I agree with Rockm, but some brands of kelp have a small but useful percentage of humic acids. Humic acids & humates do have documented benefits, saw a MI State University paper on benefits of humic acids on commercial blueberry crops. So there is some actual science. The paper mentioned seaweed & kelp, as source of humates and humic acids. Some had higher percentage than others, and similarly performed better than others. One benefit of kelp or seaweed as humic acids source is it also helps support re-establishment of mycorrhiza after transplant.
Humic acids & humates from mined sources also were effective, beneficial to the plants and the mycorrhiza.
So, Superthrive is snake oil.
Kelp & seaweed extracts are good if they contain some humates and humic acids. And if you can find other products containing humic acids & humates, even the mined sources, they will have a benefit. And because they are good for mycorrhiza, they are good to use right after repotting.
Do I use them? Yes, but I skip them when money is tight. They are not cheap, and while I think I see a benefit, it's not a huge benefit. But the work out of MSU does suggest they are beneficial.
