here is a great set of notes on making all sorts of trees and shrubs.
one of the best things i found in here was to use steel wool to make small shrubs! perfect to be able to bend and tweak after making them! even the color is pretty good gray for most small branches of a shrub w/o having to even paint it!
http://www.modelrailroadforums.com/forum/showthread.php?t=5015
cheers
jeff