Collecting plants is as much an art as the art of bonsai is. Much depends on what type of plant you're collecting, where you're collecting it and your knowledge of individual species' needs before, during, and after you dig it up. There is no set practice that can be applied for every species, or even every tree you dig. They're all different, What works for one, will kill another. It takes some experience in knowing what will work and what won't.
Books are not the best way to learn collection, as they tend to gloss over the realities involved. For instance, you will NOT get a nice rootball when you dig a wild plant. You will get a rangy, lopsided gangly root mass in most cases. Shovels are mostly useless in collecting trees. Hand pruners, hand trowels, hand held brush saws and iron pry bars are the tools that are needed.
Some vigorous deciduous species, can be barerooted and root pruned 95 percent. Others need some field soil to remain for a few years to preserve their finer roots. Evergreens from this area of the country wil die immediately if the field soil is removed--this can be a problem since some of the soils around here will autmatically fall off the roots when you dig the tree.
The best advice on collection is to find someone who has done it successfully and go collecting with them. The second best advice, if you don't have someone like that (although they're pretty easy to find in local bonsai clubs here in the Va./Md/DC area, as there are almost a dozen clubs with hundreds of members, some of whom go on collecting trips), is to experiment with lesser quality trees taken from around the same area as the plant you actually want. Dig the tree NEXT to the one you covet, see if you can get it to live for a year in a container, THEN go back and dig the nicer one.
If you dig all the good trees as a beginner and they die, you will have wasted a resource. Don't collect trees thinking they're "free." They are not. They are YOUR responsibility to keep alive. Also keep in mind that you are making an investment in the plant for the future when you collect it, not getting a "free" bonsai. You will not be able to "bonsai" it for at least two years, until it's recovered from a very very stressful situation.
All this said, permission to dig the trees is the first step. This step can't be ignored. You have to have permission from the landowner where the plant is before you start digging--of course if you own the land, then this takes care of itself
