How to keep a Christmas tree fresh for as long as possible | Popular Science
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How to keep a Christmas tree fresh for as long as possible

Help your conifer thrive through the holidays.

christmas tree next to window

Nobody wants that evergreen to go all droopy and brown-needled.

After you’ve picked over the turkey carcass and officially bid farewell to Thanksgiving, it’s time to celebrate family and togetherness in a winter way: sawing off a life form’s vital organs, dragging it indoors, and keeping it unnaturally alive for several weeks. That’s right—we’re talking about Christmas trees.

Joking aside, that “alive” part is key. Nobody wants to gather around some drooping, brown-needled vegetation. Luckily, extending the lifespans of these plants is easy—if you understand the science behind it.

The botany of Christmas

Most holiday conifers belong to the pine, fir, or spruce families of trees, although if you live farther south, you’re more likely to find a cypress. As you shop, you should check the needles to determine which species are available, because each evergreen comes with its own pros and cons.

white pine needles

White pine

On the branches of white pines, needles grow in groups of five.

Pine needles are very long—up to 16 inches on older trees—and grow in clusters of two, three, or five (which identify it as a red, yellow, or white pine, respectively) out of a single origin point; it looks a bit like a handle holds the spikes. These trees will hang on to their needles for longer than the other options, even after they dry out. On the other hand, they have notoriously sticky sap, which makes them harder to handle, and they may have slightly droopier branches.

balsam fir needles

Balsam fir

Firs have short, flat needles.

Firs have soft and flat foliage, with needles that look like they’re stuck to the branch with a suction cup. These trees boast the most aromatic smell, and they’re also likely to last the longest once cut.

Black Hills spruce

Black Hills spruce

Spruce needles sprout directly out of the branch.

Spruce needles are short and stiff, and they grow right out of the branch. These trees are a bit less aromatic than firs, so they may work better for people with allergies or scent sensitivity. However, they’re also notorious for spikier foliage, so you’ll need work gloves to handle them. Plus, they shed their needles the quickest.

If you can’t find your preferred species, don’t fret. With proper care, any of these evergreens can last for up to five weeks. However, that lifespan depends on the freshness of your chosen tree, and how you treat it.

Pick the right tree

Before you drive out to buy any holiday centerpiece, adjust the temperature of the room where you plan to store it. Keeping trees at a cool temperature will help reduce how much water they lose, which extends their lives.

Next, grab your tape measure and figure out the exact height of the ceiling in that room. Our brains are terrible at matching scale outdoors to indoors, so measuring ensures the tree will fit in your house. Check the width of your door frames too, so you’ll know which entrance to bring it through.

Once you’ve set the environment, you’re ready to start shopping. As you browse, give any tree you’re considering a freshness test: Run a branch through your closed hand to ensure the needles stay on and flex the branches to ensure they’re pliable. Also keep an eye out for discolored or overly brittle foliage, wrinkled bark, and musty odors. If you notice any of these red flags, move on to the next candidate.

When you’ve chosen a fresh-looking plant, measure the height and width to make sure it will fit into your home. While you have the tape out, find the width of its base. Live trees need a stand that can hold one quart of water for each inch of the trunk’s diameter, so a two-inch diameter means you need at least a two-quart stand. However, a gallon stand is generally enough for most commerical trees.

There’s one last thing you should do before leaving the tree farm. If you plan to bring the tree home strapped to the top of your car, wrap it carefully before transporting it. Otherwise, as you drive down the highway, winter winds can quickly dry it out. This will shorten the life of your little fir or pine—because it needs all the moisture it can get.

Plant care

A Christmas tree will die eventually, but a cool and reasonably moist environment, along with a steady water supply from which it can drink, will help it last as long as possible. Think of it as a very large cut flower, where the stand serves as the oversize vase.

When you bring home a pre-cut tree, saw off the trunk’s bottom inch before you put it in the stand (just like trimming a blossom’s stem before you stick it in a vase). A holiday conifer stays alive by drawing liquid up through vessels called vascules into the tree’s vascular system, which then absorbs water and nutrients. Once you slice down an evergreen, that cut starts drying out—within six to eight hours, the vascules at the base of the trunk clog up and the plant stops accepting water. Removing the bottom inch also gets rid of those stopped-up vessels, allowing the conifer to drink freely once more.

As you connect the stand’s supports, take care. Many Christmas tree stands use simple eye bolts that you twist until they fasten the plant in place. Help your tree out by avoiding unnecessary damage: Don’t grind the bolts into the trunk.

Once you’ve set up the stand, remember that trees get much thirstier than your average flower. Check the water level daily and refill it whenever it falls below the halfway point. On average, this happens every one to two days. However, you should still check the stand’s water daily to make sure the evergreen continues to take up fluids. If your tree stops “drinking” before the big day, you’ll need to pop it out and cut off another quarter inch.

As for potential additives, all you really need to keep your plant alive is plain tap water. You can find plenty of tales about potential mix-ins, including a combination of 7-Up and bleach, hairspray, Viagra, plant food, and aspirin. The simple truth is that none of them are meaningfully effective, as the Mythbusters memorably proved nearly a decade ago. In fact, according to the National Christmas Tree Association, those ingredients may actually make things worse.

Is there anything you can do to slow your tree’s aging? According to experiments done with balsam fir boughs, a plant hormone called ethylene, which the tree begins producing about 10 days after being cut, is what triggers it to drop needles. So interfering with this hormone might help—but that requires hard-to-obtain equipment and chemicals.

For example, some scientists extended a cut tree’s life by locking it in a gas chamber and exposing it to 1-methlocyclopropene gas. That method doesn’t exactly work at home. Another technique involves adding amino-ethoxyvinylglycine (AVG) to a plant’s water. Considering that AVG currently costs $338 for 25 milligrams (roughly the weight of a grain of rice), and handling it puts you at risk of skin irritation, eye damage, and acute organ toxicity, we can’t recommend it. Again, stick with tap water.

Fire prevention

Good news: Tree fires are rare. Bad news: As the video above shows, the consequences of this rare event can be devastating. To reduce the odds of a tree fire, you should practice good plant care and keep that Christmas mainstay well-watered.

In addition to plant maintenance, you should check your tree for freshness every couple days. Use those tests we discussed in the section about choosing a tree, and look for dropped needles, changes in foliage, and other signs of wear and tear. If you start seeing signs of drying, take the evergreen to a garage or a colder room to slow down the process.

Meanwhile, take precautions to avoid sparks in the vicinity of your tree. Before decorating it, examine lights carefully to prevent loose bulbs or frayed wires. Only use bulbs certified by a Nationally Recognized Testing Laboratory, which are labs certified by the government to test products for safety. Alternatively, stick to LED lights or smaller incandescent bulbs, which won’t heat (and thus dry out) the tree as much.

Even with well-chosen lightbulbs, make sure to read the manual closely. For example, there’s only so many strings you can daisy-chain together before you risk a short circuit. Modern lights will have fuses built into the plug, so if a string doesn’t work, either replace the fuse or throw them out.

Speaking of decorations, don’t weigh down your tree too much, at least until the big day gets close. Like any other organism, the heavier its burden, the more strain it experiences. And this strain can speed up its inevitable demise. In the time before Christmas, only hang a few light ornaments, and hold off on heavy baubles that drag down branches until the week of the holiday.

Disposal

Once the presents are unwrapped and the photos are taken, it’s time to get rid of the tree. In urban areas, check your local regulations to learn your city’s sidewalk-pickup policy. If you have a yard, mulching is a popular disposal method.

If you have the means of transportation, you can take the old tree back out to the woods and leave it there as a habitat for local critters. Or, if your town allows you to sink brush in waterways, you can weigh it down at the bottom of a pond for fish and amphibians to explore. But neither of these methods is ideal if your holiday decorations included tinsel, which can poison animals.

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