Answer: Buddleia davidii (Butterfly Bush, Summer Lilac) is available in a number of colors, and there are several considered to be "dwarf" such as those in the approximately 3 to 5 foot tall "Nanho" series. Buddleia size in general can be controlled to some extent by heavy pruning early in the spring. In colder areas the shrubs will winterkill to the ground occasionally during a severe winter and so will never reach their full potential height any way.
Among buddleias, there is also a larger tree type (Buddleia alternifolia) as well as Buddleia globosa which has orange flowers and is less hardy than the B. davidii.
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