I experimented a little with making some 1:450 trees this afternoon. As other modellers have found out, it's surprisingly easy! I decided to give Ian Holmes' method a try.
I made the trunks out of some toothpicks, which I cut into shape. The middle tree also has a side-branch, which is also a piece of toothpick, superglued to the trunk. I washed them with some black Revell acrylic paint, thinned with water. The green stuff is Busch foliage, simply attached with white glue. The results look quite convincing to me :)
Next step: actually building a layout on which I can place them ;)