Arborvitae: Taking the Lead

Q I have three 40-year-old arborvitae on the east side of the house. Two are shaded by a maple, the other gets sunlight all day and is at least one-third larger. It is also dropping needles into the roof gutter. Can an arborvitae be pruned, and when?

AYou can head back your arborvitae to a more manageable height, but it will look odd for some time.

Cut the main leader back to a large side branch, which you can encourage to take over as the tree's new leader. If the branch is horizontal, tie a stake to the trunk, bend the branch upward and attach it to the splint. This will speed its transformation from side branch to dominant leader. Spring is a good time for this.

You should make your cut lower than the desired top of the arborvitae to give room for the new leader to grow. Next year, the lateral should grow more rapidly and be on its way to filling out the top. Don't forget to remove the splint after a couple of years, when the leader will remain vertical on its own.

If you don't want to do all that, you could replace the arborvitae. There are many good varieties of Hinoki falsecypress: Nana Gracilis or Filicoides (often marketed as Fernspray) are good substitutes and remain green all winter, unlike most arborvitaes, which can turn brown in cold weather.

Scott Aker is a horticulturist at the U.S. National Arboretum.

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