Starting seedlings through holes in metal plates is not the only way to grow good nebari. I also grow many trees just by regular root pruning to control and direct root growth. Here are some photos to show that method.
Most seedlings develop a strong vertical root to ensure the little tree has access to deeper damp soil so it can survive a dry summer. In bonsai we don’t want deep roots we prefer to see well spread strong lateral surface roots. First step is to cut the vertical root. I usually look for a spot where there are several lateral roots around the trunk and cut just below.
Often I need to also remove any single higher roots. If I leave those to grow they tend to grow faster and create lopsided root system. The remaining lateral roots don’t have to be right opposite. In fact it can be better if roots on one side are higher so the seedling can be planted at an angle with remaining roots horizontal. Initial leaning trunk tends to yield a better informal upright tree.
I also cut the trunk shorter to help push multiple leaders the following summer. Multiple leaders give me better options for bends in the trunk and better taper.
These trimmed seedlings are then potted into pots for a year’s growth. After a year I should end up with something like this small trident. Note that this is not the same tree as above but it is representative of tridents after initial root pruning as shown above.
In the second winter the roots are trimmed again. Note how well the tree has responded to the previous radical root pruning with a mass of lateral roots around the area I cut last winter.
At this stage the tree can go back into a grow pot for controlled development or into the ground for faster growth. The following tree was started using this root pruning technique followed by 2 years in the grow beds. Tridents in the grow beds are dug and root pruned every winter at Shibui Bonsai