To keep your tree’s needles off floor, heed professor’s advice

December 4, 2010 at 12:00a.m.

By Karen Herzog

Milwaukee Journal Sentinel

MILWAUKEE

If you’re heading to a Christmas tree farm, heed the research of tree scientist Les Werner and his students: Keep that fresh-cut fir or pine watered once you get it home, and you’ll be rewarded with fewer needles to sweep off the floor.

Werner for years thought that keeping water in the Christmas tree stand was pointless.

The University of Wisconsin-Stevens Point associate professor of forestry never watered his own family’s Christmas trees because he reasoned trees stop photosynthesizing when they’re cut from their root systems. Unconvinced, his wife would water the tree anyway when Werner wasn’t looking.

Universities debate, research and answer real-world questions. So, who better to explore the physiology of the common Christmas tree than a scientist at the Stevens Point, Wis., university, which has the nation’s largest undergraduate program in natural resources?

“For years, I asked plant physiologists around the country: ‘Do you water your Christmas tree?’” Werner said. “Most of them, like me, said they didn’t. But their wives would water the tree behind their back.”

Werner and two students decided to document moisture loss in cut Christmas trees that were watered vs. those that were not watered. A tree farm donated 54 fresh-cut trees of four different species for a four-week study.

They set out to study whether loss of a root system, combined with an unnatural indoor environment, would severely limit a cut Christmas tree’s biological functions, including water uptake, photosynthesis, and transpiration.

Would water taken up through a cut-conifer’s conductive tissues be sufficient to replace water lost by the foliage? Would watering the tree affect needle moisture and needle-retention rates?

The research proved a direct correlation between needle retention and moisture content, Werner said. Needle moisture in unwatered trees diminishes significantly over time, while watered trees maintain needle moisture.

Based on the research, Werner advises consumers to buy as fresh a tree as they can, or to cut their own tree, if they don’t enjoy sweeping needles.

“Then make sure you give it plenty of water for at least the first week and a half,” he said.

After about a week, the tree will respond to the cut on its trunk by excreting resin, which naturally seals the “wound.” Then it no longer takes up as much water.

Cutting a few inches off the trunk before putting it in the stand opens the capillaries to allow the tree to draw moisture up the trunk and into the needles, said Werner. The water level should be two to three inches above the cut.

The study also determined which tree variety best retains needles.

They determined Fraser firs are best for water uptake, sap flow and needle retention, followed by Balsam fir, Scotch pine and Black Hills spruce.

The research has been incorporated into two forestry classes at the university.

Next, Werner wants to research whether the length of time in storage affects a Christmas tree’s moisture content, and at what point loss of moisture significantly increases the risk of combustion.

The question of moisture loss over an extended time in storage would apply to the thousands of Christmas trees that are cut as early as the end of October to be trucked to commercial tree lots, Werner said.

Here’s a little-known fact: Many Christmas tree growers apply a “needle lock” compound to trees after they are cut to keep the needles from falling, Werner said. It’s Elmer’s Glue dissolved in water.