Aspirin and 7 Up to keep your Christmas tree?

Lovers of natural Christmas trees are ready to do anything to vacuum as little as possible. Then come into play recipes from blogs or tips passed on by word of mouth to prolong the life of the tree. Adding 7 Up, aspirin or bleach to the tree water, can it really slow down the fall of needles? the Rumor Detector pondered the thorny question.

The origin of the rumor

Some of these tips have been proven… with cut flowers! Indeed, the addition of various substances to increase the longevity of flowers is used by florists and has proven its effectiveness many times in the laboratory. For example, there is a study published in Sri Lanka in 2000 which seems to show that 7 Up increases the flowering and lifespan of gladioli, while aspirin would allow roses to last up to six times longer. , according to an Iranian study published in 2011.

The story does not say, however, who first came up with the idea of ​​making the leap from cut flowers to the Christmas tree.

What science says

Researchers have been studying the question for several decades now by testing different recipes on different species of conifers. Every time, without success: no matter what ingredient is added to the water, the fir tree loses its needles as quickly as with plain water – and in some cases, the additions can even harm!

For example, this study carried out in 1991 on the Fraser fir, an important species of Christmas tree, had shown in particular that aspirin caused a massive loss of needles and that bleach affected the coloring of the fir. This was also noted by the team of the television series MythBusters, during a special on Christmas myths. Among other substances tested by the team, fertilizer had greatly accelerated needle drop.

In addition, some species will show great variation between different trees that are treated the same way, says Mason MacDonald, a professor at Dalhousie University in Nova Scotia. “With balsam fir, for example, it’s really a lottery. You could go and buy one that will lose its needles in two weeks, while another bought from the same place will keep them for six or seven weeks,” he explains.

Mason MacDonald knows what he is talking about: he studied this variety of conifers from 2007 to 2017 for his doctoral and postdoctoral studies. His work on the loss of needles in Christmas trees was part of a research program called The Atlantic Christmas Tree.

Although he was trying to determine the mechanisms involved in the loss of needles, he had also tested additions (aspirin, soft drink, sugar and bleach), since some presented plausible scientific reasoning. For example, pure sugar or that contained in 7 Up could have been beneficial for the tree, except that in practice, it rather favored bacterial development which blocked the trunk, preventing the tree from hydrating. Bleach, because it is deadly to bacteria, seemed like a good option, but the substance was detrimental to the health of the tree. In short, none of the additions brought any noticeable benefit. So we had to look elsewhere.

The researchers then pinpointed the main culprit governing the loss of needles: ethylene, the same plant hormone that is involved in the ripening of bananas and many other fruits. They discovered that by slowing down the production of this molecule or preventing the tree from detecting it, the fall of the needles was effectively delayed. In other words, it is better to take your tree for a banana than for a flower!

Industrial partners are currently working to translate this discovery into a commercial application, an additive that could be added to fir water.

The real tricks

Ensuring that the tree is always able to absorb water remains the key factor, explains Jimmy Downey, president of the Quebec Christmas Tree Growers Association.

To that end, the first thing to do, is a further cut « about an inch or two on the trunk before you put it in the water for the first time », warns Mr Downey. This is because, in the hours following the felling of the tree, air enters the exposed wood and blocks its vascular system, thus greatly reducing the fir’s ability to absorb water.

The other thing is to make sure that the base of the tree is always submerged. Particular care must be taken on the first day, when the tree can “drink” four to six liters of water. Reservoirs that are too small (less than four litres) should also be avoided, because the slightest lack or delay in watering will cause the trunk to dry out. “We would then have to make a new cut, but that’s impossible when the tree is decorated! »


The loss of fir needles is due to dehydration and the presence of ethylene. While waiting for a possible product attacking the nasty molecule, it is better to content yourself with generously sprinkling the tree with tap water… and nothing else!

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