I am just starting out as AN Allotmenteer and will be putting cardboard & newspapers into a trench to assist beans and leeks to retain water
?? DO I put them in whole or cut them up.
I tried just sheets of cardboard and as the weather has been so dry they haven't automatically rotted down so next time I will cut up small. I use my paper shredder to do paper and it is rotting down well. Make sure it is well wetted when you put it in the trench.
The main aim of this is indeed to retain water. I usually do shredder carboard and newspapers, make it thoroughly wet and put a layer in the trench (3 to 5 cm thick). This works perfect - at least on a sany soil.