Well... My first attempt was unimpressive. I've read that these can be hard to germinate but I guess I didn't fully appreciate it.
In late spring of 2016 I used 12 seeds and put them through the hot water soak twice during 2 days. They let out color and swelled nicely. Things were looking good.
By the time autumn came I had one single good looking young tree about a foot and a half tall. I'm not entirely sure that it will make it to spring because the winter has been unusually dry so far - since the last week of November we've had about 50 days of no rain or snow worth mentioning until yesterday and the top layer of soil was definitely below freezing. I'm counting on the Robinia family being tough plants.
For this year's round, here's what I'll be trying out:
- taking hot water more seriously - placing seed in boiling water then taking the pot off the stove immediately - see
http://morasc.nmsu.edu/docs/Seed%20Scarification%20Requirements%20for%20Robinia%20neomexicana.pdf
- using a nail clipper to puncture the hard shell (risky because critical parts can get clipped)
- shaking the seed in a hard-walled container at speed -- see
https://www.treesearch.fs.fed.us/pubs/31412
I hope to get at least 5 trees established and from that point onwards they sould be able to take on the task of propagation themselves.