Unrotted compost

I usually grow some early potatoes in bags using a mix of soil/compost.

Does anyone know whether the 'open trench compost' technique would work in a bag - a layer of part rotted compost in the bottom then usual mix on top?

wished i knew nightgarden,as i only use that for my beans.

Good question Nightgarden, we did spread rotted manure or part rotted compost in the potato trenches, apart from feeding the roots it also added some warmth to the soil as it worked.
The potato's grow on the Haum well up from what is in the bottom of the trench which is why we earth up and keep earthing up, saying that I cannot see a problem with doing the same in a bag.
You could try one as an experiment and let us know the result after all we gardeners spend our lives learning new tricks, the person who knows it all does not exist.

Frank.

Indeed Frank - the fun is in the trying! I'll see how it goes.