In hindsight, it may have helped if I had read two or three more, as there may be a more efficient option - but this one isn't bad either.
Start with some heavy duty scouring pads - I picked up a 4-pack of generic ones at Target for a little over a buck. These I cut in half along the long edge so that I have eight long pieces. These will be folded in half and glued together. This provides some girth and a solid base.
There's a couple insulation board walls in there as well.
After the scour pads are glued to the hardboard, it's time to paint. I simply spray the base brown - using a piece of cardboard to shield the green pad, though a little brown up the bottom is good for color modulation.
After the brown, I spray the tops with Army Painter Army Green. Again, some color modulation is a good thing.
I then add some basing material - although I may need to go back and just do all of the board on te initial one.
Another option is to add some clump foliage to the hedge for added depth and detail.
I was also recently turned on to some moss rolls or moss rope at craft stores. This has some potential for "wild" growth or other hedgerow type terrain.