Solarpunk

Thanks for the link to the Nature report. That's been my main info source for the little side project I mentioned. There are many arid-adapted trees from further south that will almost, but not quite, thrive along the Front Range due to frost sensitivity. I'm trying to observe as many of these species in real life as I can to see which might be most aesthetically desirable to a CO homeowner or municipality that wants to grow a water-wise specimen tree 10 years from now.

I had a feeling the species you were having trouble with germinating from seed was a gymnosperm. Everything you said just fits the profile of the special challenges they offer. As far as tissue culture, it's a bit of an advanced challenge since the only method that seems to work for large scale multiplication in gymnosperms generally is embryo culture or somatic embryogenesis. Frankly, those methods are hard and require a properly equipped lab. There's a lot of tissue culture you can do in a clean home kitchen, but somatic embryogenesis requires lots of growth regulator chemicals and the right equipment to maintain stringent sterility, not just cleanliness.

So, from a practical perspective, 'macropropagation' (just rooting larger cuttings really) is preferred for cypresses generally. However, even that is more challenging than most other trees.

Here's a typical somewhat current paper breaking down the extra care needed to get cypress cuttings to take root. https://riojournal.com/article/52947/

If you are ambitious or just curious, this one shows the typical protocol needed for embryo culture. It also explains in the intro the biological reason why your seed germination rate is so low. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6214434/

The last paper may guide you to finding or creating the conditions needed to get seed batches that germinate at a decent rate, yet another strategy to overcome the difficult propagation of these species.

These are only a jumping off point, the literature is massive on this topic. Hope it helps. Thanks for engaging, it's fun.