Answer: They are not toxic to other plants. The reason nothing wants to grow under them is their dense, year-round shade. I suggest people not trim the lower limbs on a magnolia, but rather allow them to grow to the ground, like they try to do. This is beautiful and solves the problem of growing things beneath them.
If you want to try to grow something beneath a magnolia, trim the limbs as high as you feel looks o.k. and select the most shade loving species, such as aspidistra (cast iron plant) or ferns.
Magnolia leaves can be composted. They will break down MUCH faster if you will break them up first by sending them through a shredder or running over them with a lawn mower.
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