@abax
Auxins are the hormones produced by the apical growth meristem in shoots that travel down and stimulate roots to grow. The most common one is indole acetic acid (IAA). There are synthetic analogs, naphthalene acetic acid (NAA) and indole butyric acid (IBA) that are well known to stimulate root growth in plants as well, If I’m not mistaken, Superthrive contains NAA and Dyna-Gro KLN has both.
As the root meristem grows, it releases cytokinins, and other class of hormones, that travel up the vascular structure and stimulate shoot growth, so you end up with a natural, cyclic back-and-forth, steady level of overall growth stimulation. When you manually apply either type of hormone, it kicks the stimulation cycle to a higher level, accelerating growth, then gradually back to the normal baseline level. From what I have read, that can take anywhere from two-, to three weeks.
If you overstimulate the plant, either by too frequent or too massive applications, it can screw up the plants’ metabolism. I have personally seen phalaenopsis flowers be deformed and ugly, and have heard folks say the same about paphs. I have also heard of stunted growth, but have not seen that first-hand. Fortunately, if you lay-off, the plants seem to return to normal. I imaging that in extreme cases it can be fatal - the herbicide 2,4-D is a synthetic auxin that stimulates the plants so much they die.
Norman’s Orchids sells Mega Thrive, which is urea with large doses of molybdenum and boron. Urea is preferentially absorbed as a foliar spray (as opposed to nitrates and ammonium, which are the preferred forms for root uptake) and the mega-doses of the trace elements stimulate hormone production as well, so the risk of screwing up the plant is also quite real. Moly also makes the plants toxic to mammals, so folks with chewing pets shouldn’t use it.
Natural hormone sources, such as seaweed extracts can do much the same, but I believe the dosage rate would need to be much greater. KelpMax is actually unique in that regard, in that the degree of stimulation is far greater than would be expected from the auxin concentration, leading researchers to credit the combination of auxins, polysaccharides, alginates and other growth stimulants for the response. Apparently, as a combination, they are much gentler on the plant than the direct applications of hormone are, and to my knowledge, no deformities have been caused by its use.
