Answer: There are many species of crape myrtle, from 40' giants to 5' dwarf and semi-dwarf plants. For your small area I would recommend a smaller variety. The following dwarf varieties grow from 3-5' and can be pruned to resemble a shrub rather than a tree:
Chickasaw hybrid; 3'+; lavender pink flowers. Firecracker indica; 3 to 5'; light red. Ozark Spring indica; 3 to 5'; lavender. Pocomoke hybrid to 3'; rose pink.
Velma's Royal Delight; 3 to 5'; magenta.
If you want something a little larger than 5', choose a semi-dwarf:
Acoma hybrid 5-10'; white. Caddo hybrid 5-10'; bright pink. Hopi hybrid 5-10'; medium pink. Pecos hybrid 5 to 10'; medium pink. Prarie Lace indica 5 to 10'; pink. Tonto hybrid 5 to 10'; red. Zuni hybrid 5 to 10'; lavender.
The roots typically grow out as far as the longest branches when planted in the ground. In a planter they will remain in the confined space. I'd recommend one of the dwarf crape myrtles.
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