Lee Valley Tools    Gardening Newsletter
   Vol. 5, Issue 4
   August 2010
   Garden Illumination: The Effects of Artificial Lighting on Plants

You could be excused for thinking that the garden-lighting trend began when those ubiquitous little solar lights surged into gardens everywhere a few years back, picking up where Christmas lights left off. I imagine the first garden lamps were candles and torches until the Victorians raised the concept to an art form. Now garden lighting is in, and it's big. It's being used to light seating areas for al fresco dining after dark; to light ponds, paths, or steps for safety reasons; to make the approach to a home more inviting for guests and less so to intruders; and to create subtle moods or emphasize architectural elements.

The Garden Lighting Trend
Want a gentle glow powered by a tiny solar panel, or perhaps a small spotlight to pick out a favorite sculpture? How about glow-in-the-dark rocks, a simulated Olympic-flame torch (they exist), or halogen ballpark lighting? It will show off the new landscaping job beautifully, but it might also encourage neighbors to call with precisely worded advice on how to adjust the intensity. LEDs, fibre optics and gas lamps are all to be had, along with the lighting specialists to help you turn your garden from a daytime delight to a place of magic and mystery after dark.

Using artificial light to create a particular atmosphere in a nighttime garden is a worthy, though sometimes elusive, goal. Plants reflect light differently under different conditions. Observe the color of a particular flower and note how the hue changes throughout the day. I have a large planter filled with a pinkish impatiens that looks quite flat during the day but becomes positively luminous at sunset. When a nearby streetlight turns on and casts its sickly yellow, sodium glow across my back garden, the colors change, and not for the better. Add the effect of the flickering neon signs from the street-corner plaza and they change again. I'm exaggerating, but balancing the subtleties of light cast in a garden can be tricky.

Effects on Plants
Before embarking on a garden-lighting system, it's worthwhile to consider the effect it can have on your plants. For low-intensity lighting that's on for a limited time, the effect will be negligible, but if you do go for the ballpark look, you'll not only be contributing to light pollution, a real problem for those who enjoy a starry night, something that's almost vanished over major cities, but you may seriously disrupt a plant's growth. This is all related to the three Ps: photosynthesis, phototropism and photoperiodism.

Photosynthesis is the means whereby a plant synthesises chemical compounds with the aid of radiant energy to provide nutrition; the equation is straightforward — no light equals no growth.

Phototropism is a plant's orienting response to light; a plant will follow the sun. Who hasn't seen seedlings straining towards the window or a field of sunflowers turned toward the sun?

The third P is photoperiodism, a plant's reaction to recurring cycles of light. Day length affects a plant's growth, especially its flowering cycle. This is why some plants bloom in June and others hang around until August. Plants can be thrown off by variations in weather such as a cold spring, which, because of a late start, will not only slow initial growth, but will cause the plant to be out of sync with the usual hours of available sunlight.

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