How to Prune Arborvitae Seasonally for Height Control
You Need Careful Timing and Technique With Arborvitae
Arborvitae (Thuja) are evergreen shrubs that often have a tall, narrow growth habit. They make for excellent living privacy screens and provide interest year-round. Pruning arborvitae is fairly easy and minimal. Only begin pruning once your shrub is at least two years old, so you don't impede its growth.
You'll potentially want to prune to maintain your shrub's neat shape, as well as to keep it at your desired height and width. Plus, you'll need to prune out any diseased, dead, or damaged branches. Winter snow and ice buildup especially can lead to branch damage.
When to Prune Arborvitae
Prune any damaged or dead branches as they arise to prevent them from breaking off and dropping on their own. Likewise, prune diseased branches as soon as possible to help contain the problem area.
Otherwise, pruning for shaping is best in the early spring, though you also can do some light trimming from spring to mid-summer. Avoid pruning later in the summer and into fall, as it can encourage tender new growth. Cold weather can damage that growth and weaken the entire plant.
Before Getting Started
It's ideal to sanitize the blades of your pruning tools prior to pruning to help prevent diseases from getting into the cuts. First, clean off any dirt and sap from the blades with a damp cloth. You can scrub with mild dish soap as needed. Then, use a clean cloth to apply isopropyl alcohol to the blades to sanitize. Let the blades air dry before use.
What You'll Need
Equipment / Tools
- Pruners and/or loppers
- Saw (optional)
Prune to Reduce Branch Length
In the early spring, note which branches you want to prune to create your desired height and width. Use pruners or loppers (or a saw as needed) to trim your targeted branches.
Avoid cutting back more than 20% of the shrub's height. And make sure the base remains wider than the top, so the lower branches can still receive sunlight.
Lightly Prune to Clean Up Growth
Anytime from early spring to mid-summer, use your pruners to trim just the tips of branches to tidy up the shrub's shape. Don't cut all the way back to old wood, as this will not regrow.
Cut Problem Branches
As they arise, prune off dead, damaged, or diseased branches. Cut them back all the way to the trunk, as they won't regrow.
Tips for Pruning Arborvitae
- Do not prune back farther than where you see stems with green foliage (unless you can live with not having a branch there at all, in which case you would prune right back to the trunk).
- Bare arborvitae branches won't sprout new growth.
- Arborvitae don't do well with rejuvenation pruning, in which a plant is cut almost to soil level in the hope that it will regrow stronger and healthier. If your plant is severely damaged, it's best to replace it. Look for a replacement that's roughly the size of your other arborvitae if you have them, so your hedge won't be unbalanced.
Does It Help a Damaged Shrub to Fertilize It?
Fertilizing is generally not recommended as a way to help damaged shrubs recover. Fertilizer is most productive when a tree or shrub is healthy enough to absorb it properly; that is, fertilization is more about “feeding” (or helping a plant take up nutrients more effectively) than “healing.”
Allow your damaged arborvitae shrub some time to heal after pruning any broken branches. Wait until you see new growth (signifying a return to health) before fertilizing. In the meantime, regularly check your shrub to make sure no fungi or other diseases are exploiting it in its weakened condition.