Avoiding Root Disturbance when planting out Beans

[George the Pigman]

Over the last few years I've struggling getting runner and climbing French beans to survive when planting out. Often only half of them survive and the others clearly have a setback with yellowing leaves. I usually grow them in RootTrainers to avoid root disturbance as I know they don't like it and am careful about planting them out well after the risk of frost in my area and always water them well after planting.
I've tried many times sowing them direct in good quality soil in raised beds but they never come up (?pests) even though the soil temperature is OK.
I am thinking of trying sowing them in a biodegradable pot then planting this in the soil but looking at the time for some of the products they are made of to degrade they degrade fairly slowly i.e. in a period of months. I would want the roots to spread out of the pot in a period of weeks not months otherwise growth would be restricted.
Anyone had any experience of using these for beans (or peas) or any other suggestions.

[JanG]

I'm surprised that you have such problems when planting out beans from roottrainers. I have grown them this way for many years, more recently in Containerwise deep cells but much the same thing.

I'm wondering whether the problem is something other than root disturbance. How far advanced are the beans when you plant them out? Have they been in their cells for too long and formed too congested a root system?
Or could you be over-watering? Yellowing leaves sometimes suggest over-watering and, although runner beans like a lot of water, French beans don't like to be too saturated.
Or too rich a soil? I've discovered over the years that French beans don't need a heavily enriched soil and think I might have lost some due to too much manure in the soil.

Sorry, I have no experience of using biodegradable pots but do feel that they shouldn't be necessary and that the problem is more likely to lie elsewhere.