In the first two years on my tenure at RC, I grew dwarf french beans, using the normal ground dwelling varieties, but I didn't really find them to be very satisfactory to be honest. They take up a lot of ground all summer, and are very delicate - even the gentlest of accidental tugs when picking beans risks killing the whole plant.
This year I have decided to go for the a climbing variety called
Blue Lake, and hope to get better results. Anticipating a dry summer, I have tried to make watering more efficient, buy burying a cheap 98p plastic bucket (B&Q's finest) with two rows of holes drilled round the sides. The beans will then be planted inside the canes, around the bucket, so that water can be applied direct to the roots, without waste and evapouration. Scientific(ish) tests show that a full bucket takes a little over 2 minutes to drain away into the soil, and this seems about right to me.
Actually, I'm pretty sure it will work OK, as I always water my runner beans from beneath, via a length of kitchen waste pipe buried in the bottom of the trench, again with holes in it. A simple "L- bend" connector, and an upward length of pipe left protruding above the soil at each end, allows me to stuff the hosepipe down to root level. A good few miniutes soak, twice a week, is far more effective in hot weather than daily surface watering. Several people at our site water their bean rows this way, and you can spot them at a distance, by the luxuriant green growth all summer long.