Oh interesting. It's arid here in the summer but wet in winter. I notice mullein comes up in recently burned soil where other weeds wont come up and eroded soil too. Maybe try scratching the soil a little first if its compact. Also cold moist stratification can help. If you don't have a cold winter or if the soil is not moist in winter when it is cold, the seed can take two or more seasons to germinate, while they lay in wait. Good luck with the controlled sowing in pots... that should work, especially if you pre strat in the fridgr! 💚🙏🏼