That shop-bought hedging looks good, but I won't have enough for the length needed and I'm not sure I can get any more so I'm trying to make something similar for myself. Here's how I'm doing it:
Start with Graham Avis textured mat and Continental Models "seamoss"
Cut the mat into thin strips and the seamoss into small branches
Soak the strips in dilute PVA glue and lay them over the branches
Fill in the gaps with various textured foams - I'm using Green Scene "Bramble", "Oak Leaf" and "Elm" and Village Models "Conifer".
I hope this suggests the slight colour variations seen in most wild hedges