The cutleaf buckthorn, or Aspleniifolia, is also known as the fernleaf buckthorn. It is a multi-trunked, deciduous, vase-shaped shrub, with narrow dark green leaves, which create a fine/ferny canopy. The cutleaf buckthorn grows well in partial shade. In landscape design it is used as a specimen tree or as a focal point within a planting. It is hardy in zones 2 to 7. You must prune in order to remove diseased, broken or damaged branches, to control its space within your landscape design, ensure safety by walkways, and to remove suckers.
Prune any damaged or diseased branch immediately, by making a clean cut at the point of the break or where it connects to the stem/trunk (diseased branches should be completely removed). Make a clean cut, if cutting it at the trunk -- do not leave a stub. You may do this at any time of the year due to necessity. Do not put any diseased plant material in your compost bin. Also, be sure disinfect your pruning shears by dipping the blades in either bleach or alcohol.
Cut away any branches that are interfering with the other elements of your landscape or walkway. You will use either the "heading" pruning technique, or the "thinning" pruning technique (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 you should cut about ¼ inch in front of the bud. This should be done in early spring when the shrub is dormant.
Prune away suckers as soon as you see them growing. Suckers grow from the base of the shrub or from the roots and deprive the main plant of needed nutrients.