I read on the forums at this time of year, mid-March say, of people who have planted their beans too early and wonder what they should now do.
Broad Beans are OK outside, but Runner Beans and French Beans need to be frost-free and, preferably, not chilly either – they don’t half sulk when they get cold, not to mention snuffing it if there is a frost
I think is will be a struggle to keep beans sown this early on tick-over until it is warm enough to plant them out, as they grow very fast. If any of them are Dwarf French growing them in pots is an option. 6-inch pots probably big enough.
Plan B would be to keep them in pots for as long as possible, then plant out, and cross-fingers that the Spring is frost free and warm weather comes early and then you will have the earliest Beans crop of anyone for miles around … but sow some more, as a backup, at the normal time just in case the early ones don’t pull through.
I have grown Dwarf French beans in the greenhouse for an early crop, with success, but I also tried climbing French beans with less success -they made an enormous amount of growth with very few flowers. The soil in my greenhouse is very rich (for the Summer crops I grow in there) so that might have been the problem.
Don’t grow Runner Beans in the greenhouse for an early crop – they need to be pollinated by Bees, and there probably won’t be any / many around early in the season. French Beans, by comparison, are self fertile so don’t need the help of the Bees