At the Scott Arboretum we have many mature hollies. Over time these majestic plants develop a broadly pyramidal habit which often spreads out at the base and can encroach on pathways, buildings, etc. Fortunately, most species of Ilex respond well to a severe type of pruning called ‘hat racking’ which rejuvenates large and overgrown hollies. We have successfully applied this type of pruning to Ilex aquifolium, Ilex opaca, and most recently to a hybrid holly, Ilex ‘Doctor Kassab’.

This practice is best completed in March. I like to step back from the plant and draw an imaginary outline of where I want to prune the tree. On a pyramidal American holly, Ilex opaca I will reduce many of the branches so the remaining habit reflects a very tight pyramid.
On March 14, we pruned our Kassab holly in front of the Arboretum offices. The overall habit of this plant is somewhat rounded so the approach was to reduce all branches by 2/3rds thus leaving a much reduced, but still rounded tree.

The term ‘hat racking’ was coined because virtually all the branches with leaves are removed leaving a skeletal network of branches which looks like a hat rack. In spring these naked branches will be covered with leaves which will emerge from latent buds on all the stems. The first growing season the tree will still be fairly open, but by the end of the next year’s growing season the tree will show very little sign of having been severely pruned.