This year we’re trying something new with our Christmas tree- we got a living Christmas tree. This means that rather than buying a tree that has been cut down and will be turned into compost after the holidays, out tree came in a pot, and after the holidays it will go out in the garden. If it survives the winter, we’ll use it as a Christmas tree again next year. In a few years, we’ll give it away to someone who wants a noble fir for their landscape. Some Northwest native trees, such as a Douglas Firs, can be donated to salmon habitat, but we’re suckers for those nice stiff Noble fir branches.
Before I spent $50-$75 on a 3 foot tree, I wanted some reassurance that I could keep it alive to reuse or plant in the future. I didn’t particularly trust the recommendations that I first turned up in a Google search, because they varied widely, sometimes contradicted each other, and didn’t differentiate California winters from Minnesota winters or Western Hemlocks from Black Pines.
Most folks assume that living Christmas trees deal with two big stressors: drying due to low humidity in homes, and loss of dormancy, or dehardening, due to the relatively higher temperatures indoors.
I’m not too worried about the issue of our tree drying out. I’ve put the pot inside a big waterproof rubber bin, both to make it easy to water the plant without getting my floor wet, and also because the red rubber bin looks festive and was much cheaper and lighter than a big red ceramic pot. I placed a few pieces of scrap lumber under the pot to elevate it, so that if water collects in the bottom of the bin, the roots aren’t sitting in it.
How long I can keep the tree inside is the trickier question, especially if I plan on subjecting it to this stress for the next few years. Some of the best research I found addressing this issue came from the folks at the Michigan State University Christmas Tree Area of Expertise Team. Most Christmas Tree research focuses on the best ways to grow and harvest trees, and leaves what happens to them after that to the consumers and sellers to figure out, so I was really excited when I discovered that this group had done an experiment to investigate the effect of indoor temperatures on living Christmas trees. I was less excited when I found out how many of the trees in their study ended up dying.
These researchers had three groups of trees: a control group, that didn’t go inside, a group that was inside for 10 days, and a group that was inside for 20 days. The groups were a mix of 3 tree species. They did a few tests on each group every few days, including testing clippings of buds and needles for cold hardiness at several temperatures. The picture from the testing of the buds and needles for cold hardiness made things look pretty good for the first 10 days, and a bit questionable for pushing things out to 20 days. After their period indoors, the trees were put back outside. Six months later, in July, the researchers noted whether the trees survived. All the control trees survived, though some of the Douglas Firs looked a bit raggedy. None of the trees that went indoors survived.
So why on earth did I buy a living Christmas tree after reading this? Some of the details of the study give me hope. First of all, Michigan winters are much harsher than Seattle winters, with average January temperatures about 20° F colder. Only a few weeks after the trees were put back outside, they were exposed to temperatures down to 7°F, which is possible, but very unlikely, in Seattle. Also, when the trees were indoors, they were kept at around 70°F during the day 66°F at night, which is about 10° warmer than my house, both day and night. I’m also planning on keeping mine inside for only 7 days, not because I’ve somehow worked out the optimal balance of enjoyment and tree stress, but because it’s most convenient to bring the tree in on a weekend, and take it back out a week later, on Christmas or Boxing Day.
When it comes down to it, though, I probably got the living Christmas tree because often the best way to find out if something is a good idea is to try it.
 N. J. Gooch, P. Nzokou, and B. M. Cregg, “Effect of Indoor Exposure on the Cold Hardiness and Physiology of Containerized Christmas Trees,” HortTechnology, vol. 19, no. 1, pp. 72-77, 2009.