So I’m in southeastern PA, I collect pretty early- usually early March, depending on the forecast. I don’t wait for the buds to swell, I collect just before. I have about a 90% success rate doing it this way, not sure if it’s because they’re a single flush or not. I collect like any other deciduous- reciprocating saw around the roots, cut the top a bit above where I want it to be, and away I go. I normally pot in a 50/50 mix of NAPA 8822 diatomaceous earth and a moisture control (peat and sphagnum heavy) organic potting mix in well draining, mostly open bottom flat planting trays, and I usually remove all native soil. I often have no feeder roots.
I let them go after that. Sometimes they won’t start to bud until June. If they don’t bud by July, do the bark scratch test but assume it’s dead. You’ll know fairly quickly if it’s going to be a good one or not- some bud all over the trunk, some only throw suckers from the roots. They do root sucker a LOT- almost as much as a honeysuckle. I usually let them go for the first year and then cut them in successive years, but don’t be surprised if you have to fight them for years. Sometimes they flush out hard for one year but collapse later on in the summer, kind of like liquidambar.
By the way- don’t stick your nose near the trunk after a chop- they smell like dog poop.