When arborvitae look shabby

Jessica Damiano | Garden Detective

June 22, 2006

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I have 20-foot arborvitae that I need to trim. When is the best time to trim them? Also, I have many decorative trees and shrubs that need the same attention.

Victoria Babich, Glen Head

The suburban Long Island landscape is no stranger to Arborvitae. The upright evergreens can be found in symmetrical rows around every corner, screening unsightly utility fixtures, adding specimen interest and defining property lines like stoic soldiers outside Windsor Castle. They grow quickly - and they're easy to grow in the Northeast - so it's no wonder they're so popular.

But what to do when they become overgrown and unruly?

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For the answer, I turned to Scott Nicolich, whose Scott Tree Company has been a fixture in Glen Head since 1988.

"The best time to trim would be the late summer or early fall - no earlier than late summer because you want the new growth to harden up and mature ," Nicolich said. "For instance, on a pine tree - your classic evergreen - the new growth, called candles, is lime green. When they become mature, they turn dark green and the needles are no longer fragile on the candle. That's when you know it's the proper time to prune."

If the plant is very healthy and you're just giving it a minor trim, he adds, the tree can handle it almost any time of year. But if you're going to be aggressive, you need to wait until the proper time, he says.

"There are different readiness signs to look for in deciduous trees - those that shed their leaves in winter," Nicolich says. "On deciduous plants, leaves harden up." A "hardened" leaf, he explains, is one that has grown to maturity and has a firm, thick padding. "If you feel a leaf in early spring, it's tender, thin and soft. As it grows and matures, its cellular growth is measurable."

If you're going to prune very aggressively, wait until the tree goes dormant, Nicolich advises. "Evergreens go into semi-dormancy if the weather is very, very cold," he says. "But you could get a warm week in February, and if the weather is 45 degrees, the tree will start to photosynthesize and grow. A deciduous tree can't do that because it won't have its leaves until the spring."

Have a question for the Garden Detective? Write to jessica.damiano@newsday.com.