Eco-gardening is at its best in The Monday Garden
January 25, 2004, Issue 96
It's stayed below freezing so that the yew bushes and SUV's are still wearing snow hats from last week's storm and there's more snow on the way. But the first signs of spring are there if you look.
Picture: two reliable indoor winter bloomers: a pink alpine geranium and yellow abutilon (parlor maple).
Outdoors, the tree buds are slowly swelling; indoors, my houseplants have started blooming again. My plants are dependent on natural light, so they don't get enough rays during the short days of early winter to set buds. Usually they quit blooming early to mid-December. Then, I'll have a glorious windowsill come February, by which time I get an hour more daylight then I do on Winter Equinox. That's seven extra hours a week, which the plants think is a lot.
In years when there's fresh snow on the ground most of the time (e.g. now), the flowers start blooming earlier because the snow reflects back enough extra light to make a measurable candlepower boost to weak winter sun. Indeed, come February, I've had houseplants burned because the sparkling snow has bounced so much sun back through the crisp, clear air.
Note that it's the length of the days (actually, the amount and intensity of light) that matters to some plants but it's the length of the nights that matters to others, just like people. Some tropical plants have little or no annual rest period; they're used to lots of light all year. Give them enough hours of light, and make it light of medium- to high-intensity, and they'll flower almost year round.
Then there are temperate climate plants that make seasonal changes to protect themselves against temperature extremes and drought. But they do it based on the light, not temperature or moisture because these latter elements are too variable. We all know about the autumn leaves changing color and then falling of due to the change in light, especial after the Autumnal Equinox when the days become shorter than the nights.
Plants that have annual clocks use light to set their clocks through a process called "photoperiodism". These plants, though, actually use the length of the nights, not the length of the days, to tell time. If you want to know how and why this happens, it's brilliantly explained (meaning: makes sense to us non-techies) in The Story Of The Flowers.
Tests have shown that the plants are definitely using light, rather than temperature or moisture levels. However, as discussed in Issue 49, I've observed indoor plants under unchanging artificial light that start growing in early spring. In these cases, I suspect that they're using the earth's magnetic force.
BTW: there's a great calculator for worldwide sun and moon rise/set times on the Old Farmers Almanac's web site.
Picture site: my diningroom window
Photo credits: Sue Sweeney
© Sue Sweeney 2005