Where did you find them? If you found them growing in the ground I would plant them into some good free draining soil and let the roots get established before doing anything too drastic.

Root pruning is the area that took me the longest too learn. If you take off too much the plant will die, if you take off too little the plant will never fit into a bonsai pot.

If you only have a small tap root to begin with, which most likely is the case if you only have 3" plants, then you don't have much root to work with. The part of the root that actually does all the nourishing for the plant is the root tips. If there aren't any feeder roots coming off the tap root and you cut the end of the tap root off then you basically cut off the plants ability to feed itself and it will die.

So if I were you I would plant them or leave them be until you get a somewhat more vigorous root system going before doing anything else.

Bonsai is an art that takes P-A-T-I-E-N-C-E. I have killed way too many plants by trying to get them into a bonsai pot too quickly.

Hope this helps some...