I'm surprised the NFG Liberation Front sow beans in pots.
For years I have sown runners and french in pots, and yes, the germination and attrition rates are good, maybe 95%. But it's a 100 pots a season with associated compost, room in the greenhouse and faff.
The last three years I have taken to direct sowing of all beans, and I've had better crops.
They have three early predators of note, mice, birds and slugs. Initial netting with enviromesh takes care of the first two, and slug pellets, along with keeping the bed a couple of metres from damp plant cover, takes care of the emerging seedlings as sure as carrot seedlings....ie about 70% survive.
My reasoning for the change was my greenhouse is full to bursting in May and there are just so many plants and seedlings to deal with. What's more, in the past, no matter how well I thought I had hardened off bean seedlings, the wind and slugs would still take their victims. I find the seedlings that emerge from the soil far more able to withstand initial weather conditions without sulking. Below are this year's runners. I sowed about 100 seeds at ten a penny on 3 May in warmed soil. They germinated under enviromesh on 17 May and they are today 5 days old as shown. Yes, there have been a few losses to slugs as they emerged and I was a bit tardy with pellets, but I will just transplant from overcrowded areas of the rows into bald patches. Bean seeds are so cheap bought loose by weight. There are about 60 emerging unscathed individuals from 100 at the moment. Plenty for my needs..
They will remain under bird netting until they need bamboo canes. Fine gauge netting can also keep most slugs at bay from neighbouring ghettos.
If I remember I'll post a photo in a fortnight of this bed and it's ongoing progress.