The German song about a Tannenbaum (a fir or pine tree) has been translated (poetically) into English with the title "O Christmas Tree". The second line reads, "how green are your leaves". But they'll only stay green if you keep the tree well hydrated.

Christmas tree stands always have a water-filled base that the tree stands in, but the water level needs to be carefully monitored, to be sure the tree doesn't suck it dry. A dry tree is dangerous - a fire hazard. The National Fire Protection Association reports that "U.S. fire departments responded to an estimated average of 210 home structure fires per year that began with Christmas trees in 2010-2014. These fires caused an annual average of six civilian deaths, 16 civilian injuries, and $16.2 million in direct property damage."

As I've previously noted in a blog entry called Christmas, my family celebrates a secular version of Christmas. We have a tree again this year, which you can see to the left. As in past years, I keep it in water by providing a larger reservoir, a rectangular box filled with water. A siphon connects it to the base of the tree stand.

You can see the set-up in the photo below. The siphon is a short length of plastic hose which connects the supplemental reservoir to the tree stand. This equalizes the height of the water in the supplemental reservoir and the tree stand. It effectively eliminates any chance that the tree will run out of water, even if it is ignored for a day or more.

The calculation:

The volume of water in a slice from the surface down to a specified depth is that depth multiplied by the surface area of the slice. So the relative volume of water in that slice with and without the supplemental reservoir is determined by the relative surface area with and without the supplemental reservoir.

The tree stand is circular, with a diameter of 8 inches (hence a radius of 4 inches). But some of its surface area is taken up by the trunk of the tree, which this year is about 3.5 inches in diameter (1.75 inch radius). Since the area of a circle of radius r is πr², the surface area of the water in the stand, subtracting the area of the trunk of the tree, is:

Computing the surface area of the reservoir is simple, as it's rectangular. Its dimensions at the same height as the top of the water level in the tree stand are about 15 1/8 by 10 1/8 inches, or about 153 square inches of surface area.

So adding the supplemental reservoir brings the total surface area of the water up to (41 + 153) square inches, which is (41 + 153)/41 = about 4.7 times the surface area of the tree stand alone. Thus when the tree sucks up water, the level goes down almost five time more slowly than had I not added the supplemental reservoir. So if, with the tree stand only, my tree were to suck up 2 inches of water overnight (about 5 cm), with the supplemental reservoir, the water level will go down only about 0.4 inches (a bit over 1 cm), a pretty trivial amount.

Since the above description of my supplemental Christmas tree reservoir is so short, I'll add a couple of additional random comments relating to this Christmas:

First: in 2016, the first night of Hanukkah coincides with Christmas eve. This is within two days of the latest Hanukkah can occur. Although Hanukkah is a specific date on the Jewish lunar calendar, it wanders around on our Gregorian calendar, sometimes occurring as early as November 28, and sometimes as late as December 27. My Christmas blog entry posted in 2013 noted that

"... This year, for the first time (and probably for the last time for centuries), the first day of Hanukkah occurred so early that it actually coincided with Thanksgiving. Thanksgiving in the United States is defined as being on the fourth Thursday of November."

So in 2013, Hanukkah was as early as it can be, and this year, 2016, it's almost (but not quite) as late as it can be.

Second: If you're curious about the lights on our tree: it's a "Tree Dazzler". You place a ring around the top of the tree, and the lights hang down on all sides (well, we moved them all to the front three-quarters of the tree). A hanging controller allows you to select various light shows, either with constant selectable colors, or changing colors. It's a bit rococo compared to our previous, classier all-white lights, but my granddaughter Darwin loves it (her hanging of many of the ornaments accounts for the bunching at a low level).

We saw the Tree Dazzler in Walmart, where there was a stack of about fifty of them, marked with a price of about $40. Margie recalled having seen them in the Christmas Tree Shop for about half that price, so I phoned the Christmas Tree Shop while standing right in front of the Tree Dazzler display in Walmart. I was informed that they were still available there, and in fact had just been marked down to $9.99 (they must not have been moving as fast as expected). Thus, returning from our shopping trip, we stopped briefly at the Christmas Tree Shop and bought one (they had a stack of about 40 of them on display). It's a lot faster to put up on the tree than a string of lights that you have to wrap around.

Since the box said "As seen on Shark Tank", I later did some Google searches to learn more about that. It seems that this is not actually the product that was on Shark Tank. That product was originally called GloBalls, from "Geek my tree". It had a lot more display modes than the Tree Dazzler, and was controlled from a smart phone app, instead of by a wired controller. Click here to see a 20115 report on its introduction (this link and the next two will open in a separate tab or window). It seems to still be available from http://www.geekmytree.com/, now called GlowFlakes, sold for $59.

So what I bought is apparently a knock-off product. It's designed and distributed by Telebrands, which has a video about it here. Of course, it's made in China. At $9.99, a bargain.

Merry Christmas to all, and may you and your tree be well hydrated.