Seeds with higher vigor produce more ethylene than seeds with lower vigor.
This here is very important to note. Seeds of high vigor, so "properly" ripened seeds, have already produced adequate amounts of ethylene and are highly primed. Further exposure to ethylene won't have much of an effect as good exposure has already occurred.
Seeds of lower vigor, such as seeds not properly ripened, or really old seeds where the vigor has dissipated, have a good chance of showing a much higher overall increase in fertility and vigor as they are either not yet, or no longer fully primed.
All ethylene really does is knock on the seeds shell and say "Hey Buddy, get your shit together, you're about to be planted" and if the seed moves some hormones around and then gains exposure to ROS (microbes) of which most healthy seeds are already packed with, presto! you get a great seedling.
The end result is quite often this....
The experiments that succeed were generally run on less than optimal seed batches, and the ones that don't show much improvement were ones trying to make optimal seeds even better.
Just so everyone knows, popping seeds in paper towels or a glass of water kills or puts dormant a huge chunk of the ROS microbes that the seed needs to benefit from the ethylene exposure. They get trapped in the paper or drown in the glass of water. Direct sowing is what the seed has primed itself for.
Also, be aware that every seed has already been exposed to ethylene before you get your hands on it, so your work has already been done for you to some degree, and it wants direct sowing.
Some seeds from some species get primed thru ripening, mainly seeds contained inside fruits and berries, and some are environmentally triggered to produce ethylene to prime themselves, such as forest fires triggering the priming of pine cone seeds.
So if you try and don't notice a difference, there's a pretty good chance you started with a too healthy of a seed, or it needs an environmental trigger.
For many species light can also be a priming trigger as it tells the seed it is now on the ground, not inside the fruit, so wake up and grow.
You can lay seeds of some species in the warm sun on the damp soil surface instead of in a paper towel, and they will prime and pop. Then bury them as soon as you notice the 1st ones starting to split.
That's how a seedling heat mat helps indoor germination. It brings the heat to match the light above. Also thats why for some species, burying the seed too deep makes it remain dormant. No light no ethylene triggering.
So you need to play around a bit before you declare failure, and victory with one species may not translate to victory in all species.
Cannabis is classified as a vegetable, so thats a good start to narrow things down.
I can tell you from both experience and side-by-sides that direct sown seeds will give you better plants in general, as in if you paper towel 100 plants vs direct sowing of 100 plants, the direct sowing will give you better plants on the average. Noticeably better.
Don't judge this part on how quick they crack and sprout, judge it on the end product.
If farmers could up their yield by paper towelling 1 million seeds they would, but they don't, so there's a pretty good indicator of the value of exposure to ROS during the process.
Those ROS are meant to innoculate the immediate soil that the seed cracks in, and get to the roots on day 1. With paper towel you toss most of them away.
Some make it and reinnoculate the soil, but that seedling is at a disadvantage already and in natures environment it would get left behind by the ones that were directly sown.
Want to see something really cool, take some spaghnum, grind it to dust, soak it in rain water to fully hydrate it, then lay a bed of it about an eighth of an inch deep on top of your soil, place a seed on it, and cover it with an eighth of an inch more.
You will need to drip or mist water on it every few hours so it never dries, but when the seed pops and the ROS inside it are released, they go into the sterile spaghnum and have no competition, thus a far greater root innoculation success.
You get really big sproutlings, or really stinky plants, and quite often both, but you also get lots of helmet-heads as soil helps remove the seed husks, spaghnum fails here.
Just don't let them dry out. It's a real PITA for 4 days, but pretty cool results.
So there are many variables at play. I'm not trying to discourage you, just the opposite in fact. If you try and fail, or succeed but can't repeat it, the reason is probably in this post is all.
Straighten that out and consider that most cannabis seeds nowadays are rushed to the consumer, and ethylene can and likely will improve things for you, you just need to figure out how to use it properly, and like always, if you encourage nature to do it for you instead of a synthetic hack, you are likely to get the best results.
A lot of seeds can produce their own ethylene, so if you can trigger that it's better than forced exposure.
