Due to the size of the layout, I anticipate that the vast majority of the trees on the NNE Scenic will be low-end commercial trees. I anticipate occasional nicer commercial trees in individual signature spots. At some point I may also try my hand at making trees as well to save some on cost, but the sheer number of trees the layout will render the time required to make trees impractical. By the time the layout is complete, I will likely need well in excess of 5000 trees.
I order a variety of both evergreen and deciduous trees from multiple suppliers in as large lots as I can find to try to keep the average price under 50 cents per tree. N scale trees are often made smaller than they should be, so the trees range between N scale and HO scale. The largest trees I purchase are roughly 4″ tall, or a bit over 50 scale feet. The very smallest trees are about 1″ or about 13 scale feet.
The tallest trees are always used near the front of the layout. As I work further back, the trees get a bit shorter to create the forced perspective sense of distance. Care is taken for trees near the track to be taller than the train, but heavily forested areas behind the track make significant use of the smaller trees blending into the background. This photo taken at more of an angle to the layout somewhat shows the height differences from the front on the right to the backdrop on the left, though even at this angle the forced perspective is fairly effective. The frontmost trees here are 4″ trees while the smallest back trees are just a little more than an inch. From the front it is quite convincing.
When I reach the top level of the layout, I will need to get even smaller trees for the sense of distance to the tops of ridges.
Bushes and other small brush use various sizes and shades of n scale bushes, clump foliage, and course turf.