Answer: These are very large trees when they mature, so please be sure you have enough space for two -- they run to fifty feet tall and forty feet wide. They will outcompete other plants for both light as well as soil space, nutrients and moisture. In general it is difficult to grow other plants beneath these.
It is better for the growth and development of the tree to limit competition at the roots by simply mulching the area beneath it. The mulch should be organic, in a flat layer several inches thick, and should not touch the trunk. As the tree grows, this area would expand.
Eventually they will shade the area so deeply that it will be difficult to grow anything between or beneath them except shade tolerant ground cover such as Liriope, Vinca minor or Hedera helix. This can be planted into the mulched area.
I hope this helps.
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