Houseplant Basics 101: Light

When it comes to houseplants, they have several basic needs: light, a temperature that is comfortable, humidity, soil, water, fertilizer and physical space. When you place all of these needs into one list, it can seem a little daunting to just cover the basic needs. However, understanding their significance requires a very small investment of your time. And when it comes to houseplants, a little knowledge really does go a long way.

I will cover each of these aspects for you over the next few days. Today we will begin with the first one: Light. Houseplants, just like people need energy to grow. But whereas people seem to obsess over avoiding carbohydrates, plants obsess over making them. I am referring of course, to photosynthesis, or the process by which plants take energy from the sun and convert it into sugars that can be used to grow. This is perhaps one of the most important chemical processes in the world.

Measuring Light

Light is the single most important factor in determining whether your houseplants will thrive or die. It is also one of the most misunderstood factors. It simply comes down to understanding that the amount of light your plants receive will determine if they are rapidly dying plants, slow-dying plants, plants that neither gain nor lose growth, slow-growing plants or rapidly growing plants.

Because light is not able to be held in your hands or poured into a glass and measured, you will need to think about it in terms of intensity, quality and duration. So what does that mean? Here is a general rule of thumb:

• Intensity of light: the strength of light available
• Quality of light: the wavelengths or colors of light
• Duration of light: the amount of time plants are exposed to light in a 24-hour period.

The relationship between these three factors is important to consider. For example, if the quality of light is high, but there isn’t much of it (intensity), pr it doesn’t last very long (duration), will your houseplant do well? Most definitely not. In an ideal world, you would want to give your houseplants the perfect intensity of the highest quality spectrum light for the optimal amount of time. But since that will never happen, you will need to compromise and manipulate it for your houseplant. Although a short burst of perfect light is wonderful, it is better for your houseplant to have 12 hours of lower quality light.

Light Factors

The greatest challenge that you will have is providing your houseplants with enough light. Although initially it may seem like a fairly easy task to provide your houseplants with the ideal quantity of light, it can actually be just a little more complicated. You may want to consider factors that will complicate and reduce the amount of natural light that gets to the leaves of your houseplants. These may include the following:

• Not as much sunlight enters your home in the winter as it does in the summer. In fact, winter light may only be 20% of the light you receive in the summer.

• Moving plants even a few extra feet away from a window will cause a dramatic reduction in sunlight. A few feet may not sound like much, but it is not uncommon to see a 100-fold drop in light when a houseplant is moved from a windowsill to a table a few feet away.

• Windows are not a source of sunlight. They merely allow light to pass through with, at best, 93% sunlight transmission. The sunlight transmission may drop to 50% if your windows are tinted.

• Windows which face the south will usually provide the greatest amount of sun exposure.

There are many other factors that may contribute to inconsistent natural light throughout the year. These include things such as fog, cloud cover, elevation, drapes and window treatments, the presence of ultraviolet-blocking coatings, dirt or dust on the window, reflections from light-colored interior paint and the presence of awnings, overhangs or shade trees near the windows.

What are your biggest challenges with light sources for your houseplants? Leave me a comment and share.