Answer: A light soilless mix would typically consist of peat moss and perlite or vermiculite. With the addition of sufficient steady daily watering/soil moisture to sustain a large tree, the weight becomes considerable. Add to that the weight of the tree and the container large and sturdy enough to hold it, and your total can easily reach hundreds of pounds per tree. I am not sure if this will meet your criteria for a lighter weight. For more specifics and typical sizes, you might want to contact your local nurseries to see some plants for yourself and discuss the possibilities. Your county extension may also have some suggestions.
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