How to choose the best Christmas tree, according to science

• Some aspects of choosing a live Christmas tree, like shape, color, and aroma, are subjective.
• But certain Christmas tree species are better at keeping their needles and holding ornaments.
• Two Christmas tree experts explain how to choose between the many types of fir, pine, and spruce.

If you're going to buy a live Christmas tree this year, there's a good chance it will be a fir. In 2019, 71% of all trees sold were firs, according to the US Department of Agriculture. The top three varieties were Fraser, Douglas, and Noble.

There's a friendly competition between Christmas tree experts over the merits of the Fraser fir and the Noble fir, Justin G. A. Whitehill, lead of the Christmas Tree Genetics Program at North Carolina State University, told Insider. "But those two are the preeminent species in the country."

Both species have great needle retention, according to Bert Cregg, a professor in the Department of Horticulture at Michigan State University. It's often a sought-after feature for those who like to keep their trees up for weeks.

Plus, the needles tend to be less pokey than those on spruce trees.

For some, though, other characteristics are equally important. "A lot of it's just a matter of choice," Cregg said, "what people like in terms of scent and shape and needle color and all of that."

What's the difference between pine, fir, and spruce trees?

One of the easiest ways to distinguish between conifer — or cone-bearing — trees is to look at the needles.

The trick to remembering the difference between spruces and firs is their first letter, "s" or "f." Spruce needles tend to be sharp, and fir are usually flat, Whitehill said.

Pines are also easy to tell apart. Unlike fir and spruce trees, pine tree needles are clustered in groups instead of individually attached to the branch.

What trees are available in my area?

Where you live may determine what type of trees are readily available. Oregon, North Carolina, and Michigan are the states that grow the most Christmas trees. "Each region sort of has their own species that they grow," Whitehill said.

In terms of firs, the Northwest has Nobles, North Carolina focuses on Frasers, and Michigan grows Douglas and Frasers, Cregg said.

Some trees are shipped throughout the US, and there's a decent chance of seeing either Fraser or Noble firs at your local lot or retailer, Whitehill said.

The National Christmas Tree Association has a map for finding farms and other retailers that sell live Christmas trees.

Which Christmas tree has the best aroma?

Balsam trees are known for their bold, long-lasting scent, Cregg said. "When you buy a candle" labeled Christmas tree, "they're usually Balsam scented," he said.

Scent is subjective, so you may prefer the lemon-scented concolor fir, for example. Those sensitive to smells may prefer a Leyland cypress, which has little aroma, Whitehill said.

The scents associated with Christmas trees tend to be woodsy or pine. "Genes called terpene synthases produce an array of aromatic compounds," Whitehill said.

Some of the typical compounds, known as terpenes, found in firs include pinene (pine), limonene (citrus), myrcene (thyme), phellandrene (mint), and camphene (camphor, a waxy substance made from turpentine). Different species have differing amounts of compounds that contribute to their scent.

Part of Whitehill's research involves looking into ways to improve Fraser firs' aroma. "We're working towards trying to develop different varietals of Christmas trees just like you would for various components of a wine," he said.

Fraser fir

Whitehill admitted he was biased since he primarily works on Fraser firs, but he said it's "considered to be the perfect Christmas tree."

In addition to its ability to hang on to its needles after harvest, the tree grows uniformly and has sturdy branches for hanging lights and ornaments, Whitehill said.

Cregg likes Frasers, too, and tends to gravitate toward them when he's getting a tree for his own home. He noted the dark green foliage and needles with a silvery underside

"It's just got a real Christmas tree form to it," Cregg said. "It just looks like a Christmas tree, and people just like that."

While Whitehill noted that the tree "smells like the holidays," Cregg said the aroma wasn't as strong as others, like Balsams.

Some of the compounds in its foliage may produce a piney or even caramel-y scent.

Douglas fir

Douglas firs aren't true firs, Whitehill said. "It's kind of in its own little group."

The trees are known for being bushy, with dark green or blue-green needles. "They'll have a very dense form to them," Cregg said. "Some people like that; some people don't."

Heavier ornaments tend to droop on their branches, which aren't as sturdy as some other varieties.

The scent of Douglas firs is distinctive and has been described as earthy, spicy, or sweet.

Noble fir

"The Noble fir is the king up in the northwest," Cregg said. In his opinion, its needle retention is even better than Frasers'.

Its needles have a bluish tint and have been compared to hockey sticks because of the way they curve. That shape also exposes the branches a bit. "It tends to be a little more open than some other species," Cregg said.

Based on its compounds, Nobles smell woodsy with perhaps a touch of citrus and mint.

Balsam fir

The main draw of the Balsam fir is its scent, both Whitehill and Bert said.

"It is a very, very aromatic fir, very similar to the aroma profile of Fraser fir, but it tends to be even stronger," Whitehill said. It's heavy on pine notes.

Its biggest drawback is it tends to shed its dark-green needles very easily.

"People really like that scent, and they'll put up with a few needles on the floor to have that," Cregg said.

Concolor fir

Two things stand out about the concolor fir. Its needles can look almost blue. And it smells like citrus fruit.

It tends to grow in a pyramid shape. "It's a really interesting-looking tree," Cregg said.

"If you crush up the needles a little bit, you'll get this really citrusy smell," Cregg said. Some people seek it out just for its scent, he said.

Whitehill cautioned that the concolor's needle retention might not be as good as other species'.

Turkish fir and Nordmann firs

Some growers are turning to Turkish and Nordmann firs because of their disease resistance, Cregg said. The two are closely related species from southeastern Europe.

"They have very, very dark green foliage" and are beautiful trees, Cregg said.

Nordmanns are a favorite Christmas tree in Europe. With good needle retention and fast growth, these trees could become more popular in the US in the coming years.

Canaan fir

Cregg called the Canaan fir "an intermediate" between Balsams and Frasers, meaning it has attributes of both. It keeps its needles a bit better than Balsams and is a little more forgiving for growers than a Frasers, he said.

Whitehill said that some retailers may label Canaans as Frasers, but their aroma isn't as strong.

Scotch (or Scots) pine

Both Whitehill and Cregg noted that Scotch pine isn't as popular as it once was. It's a tree plagued with pest issues, so it can be difficult to grow, Cregg said.

You can still find them, though. "Christmas is about tradition, and people grew up with a Scotch pine," Cregg said. "There's still a few growers that produce them."

The tree tends to hang on to its bright green needles. It has distinctive orangish bark and its stiff branches hold ornaments well.

White pine

Some pros of the white pine, which is one of Michigan's native trees, are its height and pliable needles. The needles are blue-green and tend to stay put.

However, its branches can't withstand heavy ornaments. It's a low-scent tree, which might be positive or negative, depending on what you're looking for.

Blue spruce

As their name suggests, blue spruces have distinctive blue-gray needles. "They're pretty trees, but they're very, very prickly," Whitehill said.

Cregg said you'll want to wear gloves when handling this tree or putting on ornaments. "Some people claim it will keep the cat out of your tree because they're so prickly," he said.

Those spiky needles and their stiff branches help keep ornaments in place. This type of tree seems to have a shorter lifespan and may not last from Thanksgiving to Christmas.

White spruce

The short-needled white spruce has a classic pyramid shape. Its color can range from blue-green to green to gray-green. It holds on to its needles a bit better than other spruces.

But crushing those needles leads to an unpleasant smell. "Some people will say it's akin to cat urine," Cregg said. "Definitely you want to take a whiff of your tree before you bring one of those home."