Growing Concerns: Short, dark days have role in plant life

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On the winter solstice, Dec. 21, the shortest day of the year in the Northern Hemisphere, London will get seven hours and 40 minutes of daylight.

The farther you go north, the shorter the days get, because that part of the Earth is tipped even farther from the sun. Fairbanks, Alaska, has 5.47 hours of daylight. At the equator there is always 12 hours of daylight and 12 hours of darkness because its distance from the sun never changes.

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Light levels affect how lots of plants grow. Have you ever driven past a greenhouse in January or February and they are lit up at night? This is because they are trying to trick the plants into believing there is more daylight than what is happening naturally, so they can get the plants to bloom.

This is never more important than when you are trying to grow poinsettia. In our area, if poinsettia cuttings are planted during the first week of July, they will bloom for the first week of November. There is a great deal of work that goes into getting the poinsettia to bloom.

Many greenhouses count on natural sunlight and the changing of the season to create the growing conditions for these plants. It is imperative not turn on artificial lighting, even for a few minutes, till the plants have begun to bloom. Growers use blackout curtains to block any light from outside and if they need to be in the greenhouse while the blackout curtains are in use, they use a tiny light that is only shone on the walkways, so as not to confuse the internal clock of the plants. This internal clock is why so many folks struggle to get their poinsettias to rebloom.

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The same thing can happen outside in the garden. Plants are used to their natural cycles and we add lights to our garden to light them up at night. If you have shrubs or plants that are not flowering the way you think they should, see if they are being affected by your outdoor lights. This also is why so many gardeners set up grow lights in their homes for the winter to speed things up so plants are ready to bloom early in the spring.

So, even though we are not big fans of all this darkness, our gardens and plants are using this time to rest and build the energy they are going to need for next spring.

Denise Hodgins is a professional gardening coach in London. Send your questions to coaching@diggendirtdesigns.com

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