While Japanese barberry (Berberis thunbergii) is an acknowledged invasive plant, the danger posed by its garden cultivars is unknown. This work analyzed the reproductive potential and seedling traits of wild type Japanese barberry and four important cultivars: `Atropurpurea', `Aurea', `Crimson Pygmy', and `Rose Glow'. The germination capacity of cleaned and stratified seeds was determined for all accessions in a greenhouse and seedling foliage color was noted. A subpopulation of seedlings from each accession was grown further in containers outdoors for a full season to ascertain seedling vigor. The average number of seeds produced per landscape specimen ranged from 75 and 90 for `Aurea' and `Crimson Pygmy' to 2967 for `Atropurpurea', 726 for `Rose Glow', and 1135 for wild type B. thunbergii. The vigor of 1-year seedlings—as measured by dry weight of top growth—for progeny derived from `Aurea' (2.29 g) and `Crimson Pygmy' (2.74 g) was less than `Atropurpurea' (3.45 g), `Rose Glow' (3.88 g) and wild type (3.73 g). Seedlings derived from purple-leaf cultivars displayed variable ratios of green and purple leaf phenotype correlated to the proximity and identity of likely Japanese barberry pollinators. `Rose Glow' specimens located among other purple-leaf B. thunbergii produced up to 90% purple seedlings, while other samples growing in isolation or near green-leaf plants produced less than 10% purple progeny. This suggests that some invasive green-leaf Japanese barberry could be derived from cultivars. The results also show that these cultivars express disparate reproductive potential.