Attila

Hi Degs,

Based on the colour and the density of the crown, your tree doesn't look very happy.
If I were you, I would repot it ASAP. Without disturbing the roots too much, I would shave off about 20% of the rootball and repot it in a much larger box or nursery can. If you don't do it now, you will lose another season of growth and the tree will remain weak for another year.

In good, well draining soil the trident regains its vigour very fast. Then, next spring you can do a heavy rootpruning and put it back into a bonsai pot. When strong and healthy, trident maples can take severe rootpruning.

I wouldn't worry about the hole inside the tree. You can treat the wood inside the hole with systemic fungicide to prevent fungus growing inside. You can also do the following: Fill the inside with waterproof cement, making sure that you cannot see the cement from outside on either ends (top end and bottom end). So, you would still have a hole, but just a shallow one, since the inside would be filled with cement. Otherwise, tridents are strong growers and I am sure that if you let it grow vigorously, the callus will cover the opening of the holes within five years.

P.S.: I actually like that hole, and would try to prevent it from closing on the upper end. The bottom, however, I would fill with cement and let the nebari to grow over it.