Meh, what does the internet know about stuff? Mullein is a weed in a lot of places. They say once you have it, you'll never be rid of it. If it can grow by the side of the road, it doesn't sound like a plant that needs cosseting to me.
I couldn't get mullein to grow in "nice" soil so I thought the seeds were no good and tossed them on the sandy soil. It grows great there. It has deep roots and doesn't seem to need watering (but it does like it from time to time).
It might be worth doing an experiment. Plant a few seeds in the nicest soil you have and baby the heck out of the plants, and then plant the rest of the seeds in the worst conditions you have. See which does better in YOUR conditions and adjust your growing accordingly.
Here's a giant thread about mullein
https://permies.com/t/mullein