I would say it depends on the application. I rarely prefer a method outside of aeroponic or rockwool in most settings. Pressed soil blocks are inexpensive and in-house renewable. I most often use aeroponic. I use 1-2 drops per gallon of water of SuperThrive and Bacillus Amyloliquefaciens or similar in the reservoir. SuperThrive is inexpensive, contains additional hormones applicable to rooting, contains an interesting mix of properties, and will provide the clones with nutrients.
As far as compound: Depends on the application but most often IBA as the active ingredient unless ‘hyper consciousness’ is your path in life - in which case there are other options [like organically derived IAA]. I do not have a preference between gel or powder. Once the hormone is in contact the application is complete [and quickly. The instability of these hormones / compounds is also a factor]. Powder is cheaper to ship in bulk and often cheaper in price. Aloe and other naturally occurring items have been claimed to have an impact. I most often use gel [because there are additional features often included in gel] if I use anything at all. Often, if you add V-B to a gel that does not contain it it will help penetrate the stem to deeper drive the compound but if done in powder form it will destroy the stem [as most powders, when water is applied, create a gel anyway, so this is prolonged in the cloner or indefinite in exposure if done in a cube - so never in a cube].
I allow 10-15 days for rooting in my calendars for both sanity and ample roots. I shouldn’t need to speed anything up. It also means that I do not need any ‘hormone treatment’ and I can simply allow the plants [happy and fed with SuperThrive] to root in plenty of time. That is a budget reduction and better for the environment. Allowing this length of time, in my thinking, allows me to use ‘cubes’ and aeroponic, at the same time or interchangeably, without concern. At the end of the day aeroponic has a ‘shock period’ that slows it down a moment despite the size of the roots [but picks up after that faster] and even though there are less roots in ‘cubes’ they take off a tiny bit faster [and it evens out]. As with everything else - ‘take from Peter to pay Paul’ - its a wash in my book in that regard.
Additionally adding fulvic acid to the reservoir will decrease time [and make certain one drop of SuperThrive, not two, is applied in conjunction].
I get roots, to the point of a spike, in four to five days if I include the rooting compound and at that point transplant is possible. WIthout the compound it takes approximately seven days. The additional time I allow on the cloner is to simply increase the length of the roots to my satisfaction. People claim 72 hours to transplant but I have not achieved this despite attempting a number of alternative methods. It makes me question if they are including the day that they took them. Keep in mind that splitting, scraping, or performing both on the clone will decrease time [because you are exposing cells by removing the ‘wax’ that will be reassigned to form a root]. Also, cutting the leaves of the clone by 40% horizontally will have a hormonal response [that is positive] in the clone [outside of being a good practice for other reasons]. The right amount of stem, the right shape, diameter zone, etc, all has an impact. Last, pre soaking the clones for 24 hours to prepare them for being a rootless misfit is said to decrease time - but isn’t that additional 24 hours the same amount of time as an additional 24 hours on the cloner? I have experienced no better ‘actual time’ in doing so.
I find no method is swifter than aeroponic, bubble, or fog. None of them are faster than the other. Aeroponic uses the most amount of water. Bubble and fog are about the same and need to be watched [topped off].
Spectrum matters. Make sure the light source is appropriate for root production [which becomes its own discussion sometimes]. Do not provide too much light as this will slow the process and force the clone to work harder. Distance from the light matters - far enough away but not too far [depending on the source] is a good thing.
I have propagated every which way [from glue plugs to plastic in field]. Again, it just depends on the operation, but the above is the ‘swiftist’ manner I have used.
Hope that helps.
