The crimson pygmy barberry (berberis thunbergii autropurpurea) is used quite frequently in landscape design, due to its red leaves, compact growing habit, and low maintenance. Uses range from an accent or specimen planting to border plantings. One drawback is that it has extremely sharp thorns, so avoid putting this plant where small children or pets may encounter it. Prune regularly in order to remove any diseased, broken or damaged branches, maintain its size and shape within your landscape design, and encourage and renew dense growth.
Cut away any damaged or diseased branches as soon as possible. Make a clean diagonal cut at the point of the break or where it connects to the main stem. This is a judgment call, and depends upon how it will affect the appearance of the plant. (Note: remove diseased branches in their entirety.)
Clean cuts encourage healing. You may do this at any time of the year due to necessity. Often, small shrubs such as the crimson pygmy barberry are damaged due to snow and ice, and you must prune the broken branches away in spring. Do not put any diseased plant material in your compost bin. If you have pruned away diseased plant material, disinfect your pruning shears by dipping the blades in either bleach or alcohol.
Snip away any branches that are interfering with the other plants in your garden bed, and also snip branches to maintain the rounded shape of the pygmy barberry. You will use the "heading" or the "thinning" pruning techniques, depending upon how much of the branch you need to cut away. Heading cuts are made just above a side branch, and thinning cuts are made just above a bud.
When you cut above a bud make your cut about ¼ inch in front of the bud. You can do this in spring while the plant is still in its dormant stage, and you can do it throughout the growing season without harming the plant in any way.
Remove old, woody canes located in the middle of the plant in late winter when the plant is still dormant. This removal of old wood will encourage and renew the plant to produce new growth, and you will have a much denser plant. Due to the sharp thorns, be sure to wear gloves.