Hollies (Ilex spp.) can come back from the dead — or seemingly dead — old wood at the bases of their stems. As that wood is only dormant, it is possible to cut the stems almost all the way to the ground without killing them. Such drastic pruning is best limited to southern climates. In colder zones, reduce the size of your overgrown holly gradually to cause less stress to both the plant and yourself. Most hollies actually are multi-stemmed shrubs, occasionally pruned into tree shape. They vary in hardiness from U.S. Department of Agriculture plant hardiness zones 3 to 11.
If you like, you can perform the moderate method of pruning in two steps rather than three, by cutting out half of the old stems the first year and the additional half the second year.
If your holly has been trained into tree form with a single trunk, you will need to prune it differently if you wish to maintain that shape. Thin out the canopy of the tree by removing about one-third of the weakest branches, cutting each back to the limb or trunk where it originated. Leave the main branches in place, but reduce their length as necessary to reach the desired size. Repeat this process in subsequent years.
Hollies which are cut back drastically will look bare and unattractive for a while.
Cutting Hollies to the Ground
Step 1: Disinfect Your Pruners
Dunk the blades of your pruning tools for at least five minutes in a disinfecting solution before using them. You can mix up such a solution in a bucket by combining 1 part pine oil cleaner to 3 parts of water. Rinse the tools in clean water before you begin pruning.
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Step 2: Cut All Stems Close to the Ground
Cut all of the stems of your holly tree back to within 6 to 12 inches of the ground in late winter or early spring. Make each cut at a slight angle to allow rainwater to drain off easily. Use bypass pruning shears for branches up to 1/2 inch in diameter, long-handled lopping shears for those from 1/2 to 1 1/2 inches, and pruning saws for larger branches.
Step 3: Prune New Shoots
Snip off the tips of the new shoots with your pruning shears once they reach 6 to 12 inches, to force them to branch out. Vary the height of the shoots for a more natural look, and make each cut at a slight angle just above an outfacing bud.
Thinning Hollies Over Several Years
Step 1: Cut Back One-Third of Stems
Cut back one-third of the oldest and tallest stems of your holly tree to within 6 to 12 inches of the ground in early spring. Choose stems that are evenly spaced throughout the tree to prevent a lopsided look.
Step 2: Prune Again the Next Spring
Prune an additional one-third of the stems back the following spring. Also, snip the tips off the new growth from the previous year, cutting each shoot back to just above an outfacing bud.
Step 3: Finish Pruning in the Third Year
Lop the remaining one-third of old stems off in the third year and remove the tips from the previous year's new shoots. Your overgrown holly has now been entirely replaced with new growth, but you can continue to cut out the oldest and tallest one-third of shoots each spring to keep the shrub within bounds.
- Purdue University: Pruning Ornamental Trees and Shrubs
- State by State Gardening Newsletters: Pruning Tips to Salvage Your Overgrown Landscape
- The Pruning Answer Book: Lewis Hill and Penelope O'Sullivan
- University of Georgia: Pruning Ornamental Plants in the Landscape
- University of Florida IFAS Extension: Pruning Landscape Trees and Shrubs
- University of Florida IFAS Extension: Disinfecting Pruning Tools