My runner beans have suffered in the last few years from poor pollination by bees, no doubt due to the the changeable weather.
Every DIY superstore and garden centre in my area (B&Q, Homebase, Wyevale etc) only seem to sell the red-flowered varieties of Runner Beans, which according to my gardening books need pollinating by bees.
White flowered varieties of Runner beans such as Mergoles apparently do not need pollinating by bees according to what I've read.
If all this is true, why is it that white-flowered varieties aren't more widely available?. Surely, I shouldn't have to resort to mail order to get hold of these varieties? The cropping rate of these white varieties seem to be just as good as the red varieties, so is it that gardeners simply prefer red flowers on their runner beans.
White varietes seem so fool-proof, I'm even thinking of trying some in my greenhouse where bees would be unlikely to go!
Sorry if I'm rambling on, but this has flower colour business has been puzzling me for a while. If the white-flowered ones are so good, why do we buy the red-flowered ones at all?
Difficult one this. I would erect some signs up directing the bees to your poor runner beans. Bees can, and do get lost in flight. So a little help from yourself will greatly increase the chances of pollination. Make sure you write the signs in English as you don't want cross-pollination by those nasty killer bees from Africa. Hope this helps.
I remember a few years ago we had trouble getting the bees to pollinate the flowers and we were told to mix up a solution of sugary water and to spray the plants. Seemed to work! Have never had to do that since. Good luck!
The traditional method is to tap the canes around mid-day to disperse the pollen. I now only grow Wisley Magic, red flowered, prolific and tasty, and in the past noticed no difference at all between red and white. The main reason for flower drop, if that's what you are experiencing, is insufficient, or irregular, watering.