Answer: Purple Robe Locust can grow upwards of 40' tall with a sturdy trunk measuring nearly 20-inches so the tree will eventually outgrow the grate. As lovely as these trees are, I don't think they're the right ones for your project.
Elaeagnus angustifolia (Russian Olive), or Franklinia alatamaha (Franklinia) grow about half the size of Purple Robe Locust and may be better choices. Best wishes with your project!
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