Light, Winter and Our Houseplants

Perhaps you gave your houseplants a vacation this summer by taking them outside, where they basked in the sunshine, browned their cheeks and thrived. If you’ve kept your plants indoors, they’ve still enjoyed more intense sunshine with the longer days of the spring and summer periods. Now, however, we’re back to the greyness of November and the shorter days of winter. How will our plants react to this reduction in light, and what can we do to help them get through the winter?

Light Requirements of Houseplants in Winter

In many cases, our houseplants will put up with this drop in light, if they receive enough for the rest of the year. It’s perfectly normal for the days to get shorter, or for there to be rainy or cloudy periods in their native regions. Some will go dormant, stop growing and may even lose their leaves. Before you worry, learn more about the plants you own.

In other cases, they may suffer from lack of light, sometimes to the point of death. For example, if you have a plant that prefers medium lighting but can adapt to low light levels. If it’s placed in a dark spot during the summer, when winter arrives with its shortened days, this brightness could go from tolerable to inadequate.

In short, light conditions can change with the seasons, and you may need to relocate certain plants depending on the time of year.

Degrees of Brightness

There are many ways to describe brightness levels, but let’s keep it simple with three categories: low, medium and intense.

Some books and websites add the category of bright indirect light, which is somewhere between medium and intense. Sometimes, they mention protecting them from direct sunlight. But since this category is difficult to interpret, I prefer to ignore it.

To better understand these brightness levels, let’s take a look at how they apply in a real-life situation.

Intense

Imagine a room with a south-facing window and no obstructions either inside or out. This area receives direct sunlight for several hours a day. Right in front of the window the lighting is intense.

Medium

The opposite wall of the same room is darker and receives little direct light, even though it faces the window. This is medium lighting.

Low

Does this room have a dark corner? A corridor nearby? Behind a sofa? These places probably have low lighting.

Tips for Determining the Brightness of a Location

It can be difficult to determine how well lit a place is. This is quite normal, as our eyes adapt to light conditions. If you’re in bright sunlight and enter a dark place, you’ll see almost nothing, but after a few minutes, the same place will appear bright. The opposite is also true. Imagine someone opens the curtains while you’re sleeping peacefully in your dark bedroom. The light will seem blinding!

For this reason, we often overestimate the brightness of our homes and plants. Here are a few tips to help you see things clearly.

Cardinal Direction of Windows

We often use the cardinal direction of a window to determine its degree of brightness, since in the northern hemisphere, the sun travels to our south, from the east to west. Although this method isn’t perfect, as there may be obstructions or differences due to the angle of the sun, it gives us a good indication without having to buy specialized equipment to measure lighting.

In the previous example, we said that, in front of a south-facing window, you get intense lighting. We could therefore say that a window facing east or west will receive medium lighting, since it only receives light for part of the day. A window facing the north of a building will only receive indirect light over the course of a day, i.e. low light.

But what about the opposite wall of an east-facing window? Directly in front of it, the light is medium, so we’ll go down one degree to a low level. You’ll guess that in a room with a north-facing window, there’s very little light, unless you place your plants directly in front of a window, and even then, only low light conditions. In winter, this may not be enough.

The Shadow Test

The cardinal direction of a window is a good indicator of the degree of brightness, but it can be tricky to put into practice. So here’s another technique my father taught me. All you need is a sheet of paper.

Place the sheet where you want to put a plant. Then place your hand about 30 cm (12 inches) above the sheet.

If the shadow is very sharp, it’s an area of intense light. If the shadow is slightly diffuse, it’s average. If the shadow is very diffuse, there’s only a small amount of light.

Signs of Light Deficiency

Despite your best efforts to place your houseplants in the right spot, it’s important to keep an eye on them for signs of light deficiency. Here are a few symptoms to keep in mind, taken from Larry Hodgson’s text How to Tell if your Houseplant Lacks Light?

• Etiolation: new leaves are paler and more widely spaced on the stem. The stem may be thinner than usual;
• Inclination: the plant grows rapidly in the direction of the light;
• Jaunissement: les feuilles du bas tournent au jaune et tombent;Yellowing: lower leaves turn yellow and fall off;
• No flowering: the plant doesn’t flower when it normally would;
• Rot: the base of the plant or its roots rot, as the lack of light prevents it from absorbing water normally.

If one or more of these symptoms appear, move your plant to a brighter spot or add artificial lighting. You can also remove light obstructions such as lace curtains. A good window cleaning will also increase light levels.