Posted: 07/04/2016 at 15:03
Okay, Shirley...but 30cm is quite a shallow root run. Perhaps you will be able to grow a few bunches for the house this way. Compensating for the lack of soil depth, you will need to feed & water more frequently than usual.
As you perhaps already know, sweet peas climb their supports using the tendrils they grow, so think in terms of fixing some kind of netting/trellis to the fence.
The potential height will be 2m +, but I guess yours (given the soil depth) will probably be less.