Jay

Well your discussion with 'self' was correct. They are home built. Most people use scrap wood or some buy the wood. Try and keep the box low 4-6 inches and big 1 1/2 to 2 feet square. The tree will have the positive of a large growing area without the depth. The box should have good drainage and possible a little leg thing to keep it off the ground. There have been many threads on this issue, one or two with how to's. Go to the search here and put in grow box.

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A Bonsai student living with his trees at N 44.37 W 77.49...
Think before you act... then think again... no good comes from rushing