Berberis gladwynensis

Berberis gladwynensis is one of those barberry hybrids that flies under the radar in the nursery trade, usually sold under the cultivar name 'William Penn' rather than the species name that nobody recognizes. It is a dense, mounding evergreen shrub with spiny leaves, yellow flowers in spring, and the tough constitution that defines the barberry genus. 'William Penn' grows to about four feet with a slightly wider spread, forming a tight, impenetrable mound that works as a low hedge, a barrier planting, or a foundation shrub where you want something that deters foot traffic without growing tall enough to block windows.

In Western Washington, 'William Penn' barberry performs reliably in full sun to part shade and tolerates the range of soils common to residential sites. Five diseases and one pest are tracked on this species, including rust diseases that can affect the foliage in wet springs. The evergreen foliage holds through our winters in most years, with some bronzing during cold snaps that adds winter color rather than detracting from the plant's appearance. The spines are real, wear gloves when pruning. This is a good shrub for problem sites where you need something dense, evergreen, and self-sufficient, and where the thorny nature is a benefit rather than a liability.