I have grown Dwarf Purple Queen French beans for decades.
They are easy to grow, germinate in 7 days and are a great cropper. I grow all mine in pots around the plot.
They grow to about 18 inches high, they produce lots of tasty beans from July to early October, if you sow them in early May. The more you pick the more you get over the season, an important point to remember with French beans.
Do not worry about them being Purple, as soon as they hit the water when steaming/boiling they go green.
Another dwarf variety I have grown for a few years, is Sonesta (was introduced by the good 'pass the parcel' folk on here). It is a yellow podded bean with a waxy pod and superb tasting bean. It needs good and regular checking for staking as the beans do cluster together more than other varieties and tips the plant over. Its an early sow in April as its germination and to build up a good plant to start with takes about 18-21 days. It crops July to early September.
As above I grow these in pots.
If you want a more traditional green French bean, try Opera, a quick good cropper, but treat it as I have described below with regular sowings to crop over a longer period. It gets to 18 inches high with a 12 inch wide spread. Would not recommend this for pots because of its spread.
Used to grow this as my French bean staple. But as I grow Cobra now (a climbing french bean) that is an amazing cropper, I have stopped growing Opera.
Sow this in May, June and July outside, it germinates in 7 days and crops from mid June to October with those regular sowings.
