Answer: The problem may not be a problem at all if the older leaves are dropping but new growth is evident. Broadleaf evergreen trees and shrubs naturally lose their older leaves to make way for new ones. If both older and newer leaves are dropping, the problem may be related to drainage, and perhaps some root damage at planting time. Magnolias prefer a well-drained, humusy soil of a slightly acidic pH (5.5-6.5), and moderate, consistent soil moisture. Their fragile roots are prone to transplant damage. If your magnolia was doing fine until very recently, and you've had heavy rains, then the roots may well be sodden and perhaps even rotting.
Check the leaves for signs of magnolia scale, a tiny insect that sucks juice from leaves and stems. If you find them, use a light horticultural oil such as Oil-Away from Gardens Alive (ph# 812/537-8650, firstname.lastname@example.org) to control them.
Here are general care instructions for your magnolia:
Choose a site with full sun to partial shade. When planting, make sure you place the magnolia no deeper than it had been planted at the nursery. I you plant it deeper, the shallow roots will not be able to feed the shrub. Fertilize the shrub in late fall or early spring using either compost or a specialty tree fertilizer, or a balanced granular 5-10-5, according to the label instructions.
Magnolias seldom need pruning, but if they get ungainly or you need to remove broken branches, do so after the tree is finished blooming. I hope your tree recovers!
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