A few years ago I also needed some big trees for Sherwood Forrest but never got around to doing them. I had cut a few branches off a shrub in my front garden and left the offcuts in the garage to see what the wood would do once it dried out. About a year later the offcuts had dried to a nice solid wood and all the bits of foliage had been easy to just brush off.
This shrub has now been cut down to make space for my games room so I may not be able to get more of this.
I based the trees on wooden MDF bases bought in a local craft store using a hot glue gun. I then added some air drying clay around the base as reinforcement. This was then covered in paint and sand. Now I need some foliage.
Reading about making foliage on Youtube got me thinking about making my own. The Woodland scenics packets are about $40 and would require a large amount to cover the trees. These are often out of stock and I had a supply of waste foam packing from work. I bought a blender and some craft paint and had a go at making my own. The first issue I had was the foam only got ripped into large chunks and did not look at all like tree foliage. The second was the difficulty of judging the colour as it turned out much too bright. I then squeezed out as much water from the foam as possible which also removed much of the colour!! Into the blender again but this still did not reduce the size much at all. I then stripped down the blender and using a small file I sharpened the blades of the blender. This much improved the result but was still as not as fine as the Woodland Scenics product but looks good enough.
I originally used just the black and the green paint but on the second attempt I also bought and used some yellow oxide which looks much better. The foam has not dried yet so I don't know if the colour is good enough or if I put enough PVA in the mix which means it will not clump together if the proportions are wrong.