Water will keep fickle fir happy

Extending life of holiday conifer has soaked up years of research at U.S. lab

The longevity of a Christmas tree is a function of its moisture content, and the science of how to extend the lifespan of a dying conifer has soaked up years of research by Gary Chastagner and his lab at Washington State University.

The key is to keep the tree’s water content from dropping below a threshold level. Often, a desiccated tree still has dark green needles, Chastagner said.

One test is to examine the needles. Pluck a dozen and bend them between your fingers. They should snap “like a fresh carrot stick,” he said, not “feel rubbery like a celery stick that has become limp on your kitchen counter.” The test works best with so-called true firs, like nobles, grands and Nordmanns. It’s harder to get a handle on short-needled firs like Frasers, balsams, and their love child, the Fralsam. And don’t bother with pines.

What the trees won’t tell you, the sales floor can reveal. A sprinkling of brown needles may be normal old growth from the tree’s inner branches — not necessarily worrisome. But green needles belong on the tree. Is there a mister or a hose to wet down the stock?

The firs can be fickle. A Douglas fir will stop sipping from the stand after a couple of weeks. And a noble fir may not shed even when it’s drier than a slug crossing the Bonneville Salt Flats.

Here, then, is a broad synopsis of 25 years of post-harvest cut-conifer research: Most of the true firs should keep their looks nicely if you store them continuously in water. Chastagner would like to emphasize the “continuous” part. “If the water level falls below the base of the tree for a sufficient length of time, and you put water back in the stand, it’s not going to take up water,” he said.

Every day, a tree will guzzle about a quart for each inch of stem diameter. Try to find a capacious stand. A freshly cut stem is useful, but don’t bother sawing at an angle. It’s the outer rings of sapwood that absorb the most fluid, and you want them completely submerged.

Randy Harris/ New York Times Firs, like these at Bell’s Christmas Tree Farm in Catskills, need water to thrive.