Answer: In my experience, concrete is extremely heavy and for this reason is not usually used indoors. Most indoor trees are grown in large but portable pots or tubs. For example, the popular indoor tree Ficus benjamina can reach that height and width grown in an oversized pot. This is possible because their root area is relatively small compared to their top growth. The tubs or containers or boxes are often on casters as well to make moving them aside simpler and to assist installation, removal and maintenance of the plant. If you have in mind a more permanent installation, and for some reason require concrete, you might need to check with your architect, contractor and the local building code to make sure it is allowable and this would also give you a start on your construction planning.
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