Answer: Magnolia can be grown in sun or shade. It prefers moist, well-drained, acidic soils. Once established, growth can be accelerated with light frequent applications of fertilizer during the first three growing seasons. You didn't say what you're fertilizing with but here's my recommendation: Measure an area three times the canopy spread, then broadcast one pound (2 cups) of 8-8-8 or 10-10-10 fertilizer per 100 square feet in March, May, July and September. By the fourth growing season, reduce the application frequency to once or twice a year.
If your tree has been in the ground 3 years, the root system is probably well established. I don't think it is necessary to dig and replant, but I would water deeply once each week and fertilize as suggested above. With this new regime I think you'll see some improvement by next spring.
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