The best runner beans I ever grew in the 8 years I had my allotments were grown as follows:
In the autumn of the previous year, I dug TWO ditches - each 18 inches deep, and as long as the row of runners I was going to plant. These were dug parallel to each other and about 6 inches apart. All the way through the autumn and winter, I threw all prunings, leaf clearances (non-diseased), wilted weeds (only those without seeds and without rhizomes), my vegetable kitchen waste, and anything else that rotted down easily into there. This included the newspapers I used to wrap the peelings up in for transportation, as the allotment was half a mile away and I went on foot with a wheel barrow. Non glossy magazines were also soaked in water and tipped in the hole, as were egg-shells, egg boxes and similar items.
As the 'compost' heap in the ditch grew to 12 inches high (2/3 the height of the ditch), I topped it off with 6 inches of tiger-worm filled farmyard straw/manure (which I had delivered in whole trailer loads from the local dairy farm), and then covered that over with 4 inches of soil that had been taken out of the middle of the ditch - this soil would have been between 4 and 8 inches deep in the ditch, typically what would have been turned to the top if I had single-dug the area and turned it over. This added soil made a 'heap' on top of the compost-ditch so I could see where it was at planting time.
The rest of the soil taken from the ditch was mixed with equal quantities of manure and spread on the other beds in my growing system - the lettuces I grew on it were the best I had ever eaten.
In March, when it was time to start thinking about which beans to plant, I laid black plastic over the heaps to warm the soil and help the decomposition process along.
In the middle, between the ditches, I built my bean support. Looking back on it - I was really glad I had taken the trouble to do this. as my crop would certainly not have been supported by 6 foot canes!
My support structure was made in the shape of a 'T'. A flat rectangle the length of the ditches, held up by a row of uprights all along. It took 3 ten foot long rectangles to cater for 30 foot of bean plants. The whole structure was made up of roofing timber - the slats used on the outside of the waterproofing layer to fasten tiles to the trusses - c50mm x 30mm in size. I figured they would last better in the outdoors than plain pine, having been pressure treated.
The uprights - spaced every 5 feet stood 6 foot high - this was the highest I could comfortably reach to screw it all together while standing on a wood box.
The supporting cross bars were spaced once every 5 feet - basically at each end of each 10 foot length of bar that formed the long sides of the rectangle.
Fastening the 8 foot canes to the long bars became ridiculously easy when I purchased a bulk pack of nickel plated metal spring clips - the kind you push your hammer into against a garage wall - held in by a single screw. These were hammed into place every six inches along the length of the strut with galvanised nails, tightly enough that they closed the small gap that is usually at the open side once they are installed. I wanted no gap for the cane tips to fall out of - this held all sizes cane tips securely for the three seasons that I used the frame.
I tipped the cross-support bar slightly when I fastened it to the short sides in order to allow for the slight angle between the bottom of the canes and the top of the support frame. The entire lot was designed to lean outwards at the top, so that the beans would hang on the outside of the plant foliage and be easy to pick.
When planting time came, all I did was push 8 foot canes into the centre of each ditch, 6 inches apart, and then click the tops into the tool-clips to hold them in place. Then I planted the bean seeds just next to each cane - two seeds to one cane - one in front, one behind. After sowing the 30 foot double row, I found I had some seeds left, so I went along the row, and planted an extra seed every alternate cane.
Too many for the ground, you say?! Not at all. The nutrients provided by the extra rich soil and the decomposing vegetable matter that the roots grew into made a harvest that nearly blew my mind!
I fed us, all the neighbours, and sold kilos and kilos of beans at our local WI that season. At 30p/lb (less the 5% WI takings which was taken off and the double bus fares once a week to and from the market - firstly to take the produce into town, and then to fetch back what was unsold - none-ever), I made over £150 from my bean sales at the market while they grew. I also filled three drawers in my large larder freezer, and we were still eating beans from that crop when the next lot were coming into flower the following year.
The secret was to pick them just at peak, every morning, without fail. Copious watering is essential - every day, and during the really hot summers days at night too. I helped fertilise the flowers by using a fine spray on the hose - wetting down the foliage and flowers in the early mornings and at night when they were in full flower. I had already planted Borage nearby to attract the bees and the black fly - the black fly (in theory) goes to the Borage and leaves the beans alone. This does work to a certain degree.
The fact that the plants leaned out by more than 12 inches from bottom to top (like a long, upside down right-angled triangle) meant that the beans pretty much hung clear of the canes, making harvesting very easy. The beans grew more than 9 foot tall, but when they fruited at the tip section, the weight of the fruit meant that the beans hung down and over space, enabling me to pick them if I stood on my trusty wooden box.
At the end of each row, I allowed a few plants to run to seed and dry out - these were my seeds for the next and following years until I moved house and had to give up the allotments.
It was runner bean heaven. And that is how I have grown my beans ever since.
This method works as well on climbing french beans as well as long runners.