I am sorry for this delayed reply to your gardening question. We are transitioning to a new Q&A system and your question was unfortunately lost in the transition. I have discovered it now and hope this reply is not too late to be of help.
Southern magnolia is not particularly adapted to the south Florida area. Florida Extension recommends it from north to central Florida. If you want to give your plant the best chance, mix 3 inches of compost in a large area (10 feet or more wide) then plant the tree in the mixed soil. Keep the roots moist but not soggy and after a couple of months begin light monthly fertilizer applications.
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