My next door neighbor moved away and no one mowed her lawn. In the Pacific Northwest that’s a no-no. It doesn’t take long for the grass to envelope a house. Within a short period of time it had reached 3 feet in height and gone to seed. I knew the real estate agent wouldn’t stand for it much longer and so struck out into the “forest” and began taking selected “clippings.”

This is much easier than Walnut tree branch models because the actual “build” is nothing more than clustering a bunch of these “weeds” together in an appropriately sized bundle and gluing the bottoms together. I used everything from 5 minute Epoxy to Elmers white glue successfully. I believe matte medium would also bond this stuff together although it would take a long time to do so. Use small spring clamps like modified clothes pins to hold them while drying.
I use matte medium to coat each individual stem and set all of those aside to dry. While you are watching that happen you can decide if you need color or leave them natural weedy brown. I use acrylics. Try to be very subtle if you color them.
I use brushes to apply the paint in washes as it gives me the kind of control I need for this really “close” work. An airbrush might come in handy though for overall coloration or highlights.

Keep looking for opportunities. No matter where I am I’m always on guard for modeling applications from the environment. I’m always pleasantly surprised when I find them too.
Try to make these “bushes” smaller than your main trees and foliage. They are underbrush or at least that is the way I use them. If you have a better use for them have at it!
When they are all dry, plant them with a dab of glue in a pre-drilled hole . Be sure to brush dirt (ground cover) around the base to give them a “planted” appearance.
Best of all, this stuff is free!!