I don't think that book has the BT article in it about exposed root pines. There was an exposed root article in the same issue as the Pine-from-seed article - I think that's BT #22 (I had a copy but can't find it now). It's a shame you didn't ask a month ago because I just started about a dozen more of them and I could have taken photos. But a basic overview would be something like this:
Start ideally with a 1- or 2-YO pine seedling -trim any long roots so that there is a small circle of roots, they should be relatively evenly spaced and come out of the bottom of the trunk all at or near the same place and at a steep angle. Meaning that they should not look like roots on an informal upright or other bonsai where you want them to exit the trunk and form a perfect spread. instead you want the roots to look like they flow into the trunk so that later it becomes harder to pick out the junction.
I use a pond basket - square, about 12 or 13", probably equivalent to about 2 gallons as the base container. Then I take a one gallon container and cut the bottom off of it to form a tube. I anchor that to the corners of the pond basket and bury the bottom edge about an inch below the soil line in the pond basket. Sometimes I use two 1-gallon nursery containers with the small ends both cut off and then stick them together to make the tube.
Fill the pond basket with bonsai mix, the normal stuff that you use. Then fill the gallon container with a mix of large and small pumice. You could use other materials but pumice wont retain nutrients so the roots will grow through it into the bonsai soil. You can use lava rock or even pebbles or whatever...the key is that there be particles up to about 1 inch in size or even a bit larger, you could put rocks in there if you want. This causes the roots to have to go around the particles so that they are not all straight when you expose them later. You don't want big air pockets in the soil so mix smaller particles down to about 1/8 inch in between.
Leave a couple inches of space at the top of the tube - take the seedling and hold it in the middle of the tube. Add bonsai soil around it until you fill the tube to the top. Anchor it in place with something from the top. I use guy wires attached to the copper wire that I use for shaping the trunk. Do not try to anchor it from the bottom as you would a mature bonsai because you want the roots to grow freely.
Let the tree grow for one season and then start removing the tube. Keep in mind that the height of your tube above the base container will determine how much root you are exposing and thus the height of your "trunk".
Here are a few examples:
The largest of the ones I posted previously. Note that after exposing the roots that grew through the pumice I bent them to the side. Often the roots will have some small movement from the soil but no larger movement so you can stake them or try to wire them to add a curve or twist after they have been exposed.
From the top - notice how the roots are not spread but flow into the trunk smoothly
Most of the rest of these are three years old. Here is one where I exposed the roots last year but decided that I wanted them to be longer so I put it on top of two more gallon containers this winter so that I could expose more. Dont forget to wire the new growth to harmonize with the roots.
On this one I originally spread one root away from the others and twisted a bud through the gap so that the tree would be intertwined with itself
If you have a 3-YO or a tree that already has longer roots you can try wiring them as a clump to make your trunk. This has it's drawbacks in that it's easy to create reverse taper in your "trunk"
Same tree from the top:
Chopsticks stuck in between the roots on this one to spread them apart.
This one started as exposed root when it was 2 months old - but I decided to extend the roots slightly so put it in this container.
Hope that helps. Personally, other than the large pumice or lava part - the most important thing is to just use your imagination and experiment with things. Remember that you'll always thank yourself later for adding a twist or curve to something young and pliable.
Cheers,
Eric
