Night Lights

A well-lit garden path can be a pleasant experience on a summer evening, but what do those lights do to your plants? Let’s find out.

Landscape lighting (Asaph441) CC BY-SA 4.0

Natural cycles

Light at night is not natural. Nothing, us included, evolved to deal with artificial light at night. And we are all light-sensitive to one degree or another. Chickens produce more eggs in summer when their chicks have the best odds of survival. So chicken farmers put their hens under lights to get as many eggs as possible, as quickly as they can. This arrangement works well for the farmers. But it is hard on the hens. Left to live a natural life, the average hen can live 10 to 20 years. Commercial hens generally live only 3 to 4 years. All of those lights and productive demands are hard on people and plants, as well.

Well-rested hens are healthy hens

Commercial egg production (Jean Beaufort) PublicDomainPictures.net

Sources of night light

There are many sources of artificial light at night. Street lights, porch lights, decorative path lighting, and security lighting are the most common sources of light at night. Depending on where you live, headlights, factory lights, and strip mall lighting may also be sources of artificial light for your plants. And indoor plants are subject to our overhead lights, reading lamps, and computer and television screens. It’s a wonder anything gets any sleep these days!

Natural cycles

The natural cycle of light and dark triggers circadian rhythms within us that allow us to sleep, repair ourselves, and recover from the demands of our days. Plants have similar needs. While plants use sunlight to perform photosynthesis during the day, they need darkness to produce an important compound called phytochrome.

What is phytochrome?

Phytochrome regulates several functions within plants, including abscission, dormancy, photoperiodism, and seed germination. Without healthy seed germination, our gardens might be rather dismal places. And photoperiodism allows plants to anticipate the seasons, triggering them to bloom, grow, and rest at the proper time of year. That is where ‘short day’ and ‘long day’ varieties come in. They use photoperiodism to tell them if the correct balance of daylight and darkness hours is right for them to bloom and grow safely.

Plants need darkness to stay healthy (Pixnio) Public Domain

Plants are much more sensitive to the number of daylight hours than you might expect. For some plants, as little as one-minute exposure to a 25-watt bulb is enough to halt blooming. Strawberries are very light-sensitive. If they don’t receive enough darkness, you might not receive any berries.

The number of hours of daylight can also cause bolting, which can shorten the useful life of your lettuces and spinach. If bolting is a problem in your garden, you may want to turn off some of those lights.

Abscission and dormancy

As the days get shorter and the nights get longer, plants produce hormones used to protect themselves through the colder winter months. Those phytohormones tell plants to pull nutrients out of leaves and let them fall. If any part of that natural cycle is interrupted or interfered with, plants can be unprepared for winter weather, making them more susceptible to pests and diseases.

Night lights and insects

We all know that moths are often attracted to porch lights, but nighttime lighting attracts several other insects to our landscapes. Research from the University of Exeter has shown that night lights “trigger complex effects on natural food webs [and that they] may have more permanent, widespread impacts on wildlife and ecosystems.”

Managing light pollution

Now we know: too much light at night can adversely affect our plants. So it’s up to us to reduce light pollution (and air pollution) to improve the health of our plants and the food they produce for us. Try some of these tips to help reduce light pollution in your home and landscape:

1. Eliminate 24-hour security lighting and replace it with motion-sensor lights.
2. Turn off unused lights.
3. Use fewer lights both indoors and outside.
4. Close your curtains at night.
5. Turn off all lights when you go to bed.
6. Use night shift settings on all your devices.
7. Use dimmers and timers.
8. Point exterior lighting fixture straight downwards rather than at an angle. [Your neighbors will thank you, too.]
9. Use LED lights.
10. Reduce nighttime driving.

With a good night’s rest, you and your plants will both feel better.