Nightlength Sensitivity in Houseplants

I think I’m going to have to reset my plant lights if I want my Christmas cactus to bloom.

One of the plants I ordered from Logee’s last fall was a Christmas cactus, “Christmas Flame,” with beautiful peach-gold flowers – at least, according to the catalog picture. It’s healthy, glossy, and generally looks as if it really enjoys my cool plant room, but there’s not the slightest sign of buds. And I’m afraid I know why.

Christmas cactus are day-length – or more accurately, night-length — sensitive. They need cool temperatures and at least 12 hours a day of uninterrupted darkness to form buds. Cool is fine; my plant room is thermostatted to 65° daytime and 55° nighttime temperatures. Night length? Well, I’ve had the lights programmed to be on 16 hours a day, to make up for the fact that at this time of year the plants are almost totally dependent on artificial light. Cool temperatures alone are enough for some cultivars, but apparently not for this one.

So I’ve reset the light cycle so the lights go on at 8 am and go off at 8 pm. I’ll have to keep the door to the plant room closed in the evening, and I may have to move the plant away from the window for the next full moon. (Not this one; we’re predicted to have cloudy skies for the next few days.) I don’t think the snow reflects enough light from my bedroom window to be a problem, and the nearest street light is at least a tenth of a mile away and not on the same side of the house as the plant room. Aurora? Not likely to be bright enough to cause a problem.

Supposedly it takes 6-8 weeks of long nights to get the buds going, so it’s likely to be February before I know if my cactus is going to bloom. Meanwhile the jasmine has put out a flower, the first narcissus opened today (and I can actually smell it) and the potted rose bush is putting out a new flush of growth. It may be winter outdoors, but the lights and the plants are going great indoors.

Fairbanks Weather 9/12/11

Sunrise was at 7:04 this morning and sunset at 8:29 this evening, for a daylength of 13 hours 25 minutes. We’re losing 6 minutes 39 seconds a day. The sun at its highest is a little more than 29° above the horizon, and now dips more than 18° below the horizon — astronomical night. At the same time the full moon, which of course is opposite the sun in the sky, is getting higher in the sky — almost 25° tonight. The last quarter will be higher yet.

Amur maple in my yard. It has some anthocayanins, but as an exotic is slow to turn color.

I put the plastic covers over the beans and squash last night, and brought in the geraniums. The late-planted green beans are almost ready to pick, and as this is a new variety for me, I at least want to find out what they taste like! Turned out it wasn’t necessary, though, as the temperature at sunrise was 36F.

The trees are at that stage where some are green with just a few yellow leaves, some are about half turned, some are all gold, and some are already turning tan and losing their leaves. Yellow leaves sprinkle my lawn. There are even a few clumps of red-orange on the hillsides.

Clumps? Yes. Aspens, like birch, normally turn yellow in the fall, not orange. But a few mutant aspen do show a lot more red than usual in their foliage. Single trees would be hard to spot, but aspens spread by growing new shoots from their roots. This is decidedly problematic when you have a lawn bordered by aspens; trees are constantly poking themselves through the grass. But it also means that a stand of aspen is often actually a clone, each tree identical to its neighbors genetically. If one of the mutant trees with more red than usual in its fall coloring starts forming a spreading clone, the result is a red patch on the hillside.

The photo, looking ENE from a parking lot on the north side of Fairbanks, shows two such clones on Birch Hill. The more obvious is on the right side of the picture, just below the horizon. The other, smaller clone, is above and to the left of the Home Depot sign. More than likely, the uniform light green areas are other clones, ones that turn color late.