Trimming your holly tree helps to maintain its shape and encourages new growth. Limit major trimming to the tree's dormant period. Wear appropriate clothing and eye protection due to the sharp spines on the holly leaves.
Inspect the holly for disease
Look for wounds on the tree trunk, which are a sign of a disease. While a mild infestation is treatable using an appropriate pesticide, consider removing any tree with a major infestation. Dispose of diseased debris in an appropriate manner to prevent infestation of other trees in the area.
Choose the most appropriate method for your species of holly
Trim hollies that form a rounded crown and grow to at least 8 feet tall by limbing up, removing lower branches to form the bush into a tree. Trim conical hollies using hacktracking, a method that involves trimming all limbs by two-thirds, to reinforce the shrub's pyramidal shape.
Select the branches to trim
DoItYourself.com recommends removing any branches growing upward or downward when limbing up, leaving those growing horizontally. Trim any damaged limbs and those that appear to be weak. Beginning at eye level, remove branches that cross and thin any dense growth to provide air circulation. Keep the lower branches longer than those above them.