The 2012 ASHS Annual Conference

Japanese barberry (Berberis thunbergii) is an invasive shrub across most of the northeastern and central United States, but it is also an important landscape shrub. Using a replicated field planting we evaluated the fruit and seed production of 46 cultivars. A subset of popular cultivars was evaluated to determine how well their seeds would germinate and survive in a dry deciduous woodland. Cultivars produces as many as 12,000 seeds per plant and the number of seeds per fruit ranged from 0.1 to 1.8. Five cultivars produced fewer than 100 seeds per plant and two cultivars failed to produce fruit. In general, yellow-leaved and dwarf purple-leaved forms produced less seed than green-leaved cultivars or standard-sized purple-leaved cultivars. Fruit production increased to as much as 35,000 fruit per plant when plants were allowed to mature for 4–5 additional years. The two cultivars, which appeared sterile at the initial evaluation, produced small numbers of fruit when they were more mature. It is clear that sufficient time must be provided for woody plants to mature and establish before they can be useful in accurately assessing cultivar reproductive potential. Cultivar seeds germinated between 12.5% and 31% when sown in a deciduous woodland and exhibited survival rates between 5.6% and 29.3%. We combined germination data with survival data to generate a predicted establishment rate for each cultivar tested.  The predicted establishment rate was then used in combination with seed production data to estimate the number of seedlings that each cultivar has the potential to contribute to a natural area annually. Even cultivars producing as little as 100 seeds annually have the potential to contribute a few seedlings each year to a natural area. Since barberry is a long-lived woody perennial, the number of seedlings an individual plant could contribute to a natural area could be quite high, even for cultivars producing low numbers of seeds.