Ola Sammy
Well it kinda depends on what you are looking for. If it is for a diorama it can be everything. Look around in the forums a bit and you will probably find a lot of articles on how to make bushes, Trees and other foliage. Check the diorama Section.
If it is for Camouflage on German Vehicles then you have a couple of options. You can invest in some PE (Photoetch) foliage. It comes in Different shapes and sizes and even different kind of trees and such... Down side is that it is kinda expensive but it looks cool.
Another is taking a small branch from your garden and glueing Birch seeds on it. A birch seed has a very nice shape which does a good job as a leaf in 1:35. problem is that often you have to glue the Birch seeds on it one by one which is a long task If you look at the picture below:
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Here you see an Ivy growing through a 37 mm PAK. The branches are made with sewing thread and the leafes are glued on it one by one.
Another trick is using grass. Now I`m not talking about the Illegal stuff. I`m talking about the grass you will find just next to the road. It simply looks good in scale. I can`t say more about that. I knowq a guy here from Holland who uses it a lot as Camoflage on vehicles an example can be found here:
And best suitable for a winter scene is the use of Asparagos for Foliage. An example can be found here from the same modeler:
Asparagos can be found in almost any flower shop. and it looks like Pine tree branches already.
I hope you can do something with this information.