Answer: The problem that I see with sinking them in holes is that they may root into the ground thorugh the drainage holes -- making it difficult to bring them indoors again the fall. Also, the holes may fill with water when it rains, causing drainage problems for them as well. So I don't think I would recommend it.
Perhaps you could tie the containers down by lashing them to a railing or set concrete blocks around the base of their containers to help hold them steady instead. Or, if you have ground to work with, tie the container to a short but sturdy stake or two pounded into the ground. If you set the pots on bare ground you will need to turn them often to make sure the plants do not root down into it. Good luck with your trees this summer!
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