How early can I plant runner beans?

Last year my  Sunset Runner beans barely survived the summer, then they grew very well and produced a few beans before frost.  I want to plant them as early as possible this year.  I can’t find any information on soil temperature needed for germination.  Can they survive any frost?  Are they hard to transplant?

I liked the flavor and texture of these beans much better than the usual bush beans.

My great grandfather said, take your pants down and sit those cheeks naked in the soil.  If it feels cold, it's too early for runners. About 20 degrees C is the ideal soil temp.

My own experiments planting each week, show that the beans I planted 6 weeks early produced beans 2 weeks later than following the recommended time.  They did survive some frost, but grew so much slower than those started in warmer soil.  

I have poor luck transplanting runners, but they do sell starts in the nursery,  so I'm guessing some people find it helpful.

But that's where I live.  If you can, do your own experiments to see how it grows in your climate and soil.  Where I am, the local seed company puts out planting charts for different regions,  so I use that as a starting place or about 2 weeks before regular beans.

70 * farenheit soil temp.

Jeff Peter wrote:70 * farenheit soil temp.

At what depth?
At what time of day/night?