Best way to develop radial roots on small trees?

I have about a dozen small trees that I would like to put in the ground to develop and thicken up. However, like many young trees, their roots are not advantageous for bonsai. I need to do something to establish good surface roots. I could either use the tourniquet method, the girdling method(in the ground) or I could simply cut off the taproot and plant the tree on top of a tile or a plastic plate. The first two will probably require me to come back in a year or so and remove the root system below the tourniquet/girdle, but I think they will be the safer bet for the health of the tree. Of the three, which do you think will be the better method?

How small?

JimLewis wrote:How small?

Most are 4 to 5 feet tall, and 1 to 2 inches thick at the point I'd attempt to build the new roots.

Oh, wow.  That's huge to me!

I guess "small" is a relative term <g>.

Personally, I think the girdling process is the most reliable.