Why the incredible range of advice on U. parv stratification?

[alphaparrot]

I'm relatively new to bonsai (about 1 year), and am left puzzled by the range of advice on whether and how long to stratify Chinese elm seeds. I was recently sent a free packet of Chinese elm seeds with a pot I ordered from a local bonsai supply company (only place I could find an appropriate rectangular pot for a rootbound jade I was repotting), so I figured eh, they're free, so why the heck not give 'em a try.

And therein the confusion starts. The company that sent them says to cold-stratify 30-60 days. I've seen other resources online say 90 days. Yet others (including on this forum) say they don't seem to need any.

So I'm curious if anyone has any ideas as to where this variation is coming from. Is it that this is a naturally hardy tree (suitable to a wide range of USDA zones), so some parent populations are adapted to little winter to speak of and don't need stratification, while others have relatively harsh winters and won't germinate until they've had 3 months of cold, and it's just luck of the draw which seeds you get?

My assumption is that they must need *some* stratification, because while other elms seed in the spring (and thus must germinate quickly), chinese elm seeds in the fall (so seeds must wait). But is even that observation just specific to *some* chinese elms?

I've been working with planted aquaria for about 8 years, long enough to observe that often the 'conventional' wisdom about a plant is simply a shorthand for the application of a more-fundamental principle related to its needs, made to fit a particular non-natural environment. For example, some aquatic plants are considered "difficult" without injecting CO2 into your aquarium water, but if allowed to grow in conditions more like their wild habitat, and in their natural/wild form, will grow like weeds without any intervention. Is the wide range of experiences with Ulmus parvifolia similar, where really we just have a lot of people finding rather different shortcuts to triggering whatever happens in the wild for these trees?

For me personally, I'll just cold-stratify in a plastic takeout bowl in damp loam+perlite+sand for a month or so until we break out of the coldest winter temps here in Toronto, and if they haven't sprouted, then put them outside for a bit to see if a daily temperature cycle is part of the equation.

 

[Wires_Guy_wires]

Is the wide range of experiences with Ulmus parvifolia similar, where really we just have a lot of people finding rather different shortcuts to triggering whatever happens in the wild for these trees?

The answer is yes. Chinese elms are so easy that everyone who tries a different method can be successful in the 80-90% germination range, which is mostly dependent on seed quality and not germination method.
So everyone reports their method as a good method.

Local elm species here germinate whenever the seeds hit the soil, or the roof, or the pond, or get stuck in a car door rubber.

 

[Shibui]

So I'm curious if anyone has any ideas as to where this variation is coming from.

Some companies have a 'standard' advice they apply to almost all seeds. As @Wires_Guy_wires says, most seed grows despite what we do to it rather than because of what we do.

Note that it's native range is temperate to sub tropical Asia which may be why it seeds in Fall. It probably hasn't needed to develop winter dormancy in the seeds. It also naturalises in many warmer parts of the world which would also indicate no need for stratification of seeds.