Let's Talk About Phototropism

If your plant is exhibiting awkward growth, it's probably a cry for sunlight.

Tall, leafless growth? 

Pale leaves? 

Curved stems?

At some point, every plant parent will see the effects of phototropism or etiolation: common plant problems that result from too little sunlight. In addition to water, all plants need light in order to perform photosynthesis and create the energy they need to survive. If your plant is deprived of sunlight, it will physically adapt in hopes of reaching more. 

Growth will get unusual when your plant is struggling, and you’re bound to notice changes in its healthy appearance as it does all in its plantly power to survive. Hopefully, you’re reading this before it’s too late. (*Siri, shuffle songs by Drake.*)

In this article, we'll get into the science behind phototropism and etiolation, and check in with Plant Next Door’s horticulturist to learn how to best move forward once you notice the symptoms.

Phototropism: Stretching Towards Sunlight
When your plant is craving more sun, it will focus its energy on growing towards the nearest window. This is a surefire sign it's experiencing phototropism: a directional response that allows it to grow towards a source of light. 

To understand phototropism, you must first understand auxin: the plant hormone that influences the elongation of plant cells. Greater quantities of auxin are produced on "the darker side" of the plant, causing the cells there to grow larger than corresponding cells on "the lighter side" of the plant. This ultimately curves the plant stem tip toward the light, and elongates the shaded side more dramatically. 

There's a difference between plant behavior when light is lopsided vs. when it’s simply insufficient. If your plant is not getting enough light, it may be experiencing etiolation.

Etiolation: Struggling For Survival
When plants don’t receive enough sunlight, auxins are transported downwards from the actively growing tip, ultimately suppressing lateral buds. The auxins stimulate proton pumps in the cell wall, which increases its acidity and triggers an enzyme that ultimately weakens it. (source: https://www.gardeningknowhow.com/garden-how-to/info/what-is-etiolation.htm)

This increases its chances to reach the light by focusing its energy on growing taller, but results in unsightly symptoms like unusual lengthening of stems and leaves, elongated internodes with fewer leaves, paleness, and weakened or collapsed new growth.

Now that we have an idea of what’s happening inside your pale or leggy plant, let’s propose some steps forward.

Lesson #1: The Right Window Exposure is Key
The first and most obvious element to consider is where your plant is positioned in your home, so you can assess how much light it’s currently receiving. There are a few different ways to measure light intensity, but determining the window orientation closest to your struggling plant is a good place to start. 

Here’s a quick breakdown of light intensity relative to window orientation in the Northern Hemisphere:
North-facing windows: Not generally your best choice, these windows have the weakest light intensity and are usually not conducive to plant growth. A shade-loving plant may do fine, but tropical plants will likely suffer from this level of sunlight.
South-facing windows: Typically the brightest spots in the house, south-facing windows are perfect for sun-loving plants as they offer the strongest light intensity.
East-facing windows: This exposure is good for plants that require moderate sunlight, as East windows get morning sun, when the rays are not as strong as later in the day.
West-facing windows: With full afternoon and evening sun, this is your second-best choice for sun-loving plants. Not quite as intense as a southern exposure, yet usually bright enough to sustain most common houseplants.

Consider moving your plant to a southern or western exposure to increase the amount of sunlight it’s getting, and keeping it as close to the sill as possible.

Tip: Healthy plants will also stretch in one direction if their light only comes from a single source, making it important to rotate your plant regularly to ensure even growth. Try giving it a quarter-turn each time you water it. 

Lesson #2: Add Fluorescent Light When Needed
Supplemental light can be a great addition for the more serious plant people out there. Even in spaces with large windows, other factors can impact whether your plants are receiving the light they really need. 

According to our horticulturist, the ideal lighting for smaller plants on a windowsill are T5 fluorescent lights. They have a great, broad light output while remaining fairly streamlined in appearance compared to lights in the same family. One important factor in using fluorescent bulbs is that they produce a fair amount of heat.

This can be beneficial at times, but it is important to keep in mind so you can adjust your watering practices and be aware of the humidity levels—they might dry out faster than usual. Full spectrum LED lights are another option. They run much cooler and can be great for individual specimens or smaller areas, but are considerably more expensive.

Lesson #3: You Can’t Save Them All
With succulents and cacti, unusual growth may be fatal. When plant parents keep traditional cacti and rosette succulents like echeveria in insufficient light, they often start to stretch and form peaks. Unfortunately, this is not reversible in the same way that a tropical foliage plant may grow out of its weak growth when provided the light it requires. 

In many cases, plants can die from etiolation, so it’s important to prevent it from occurring in the first place. Use our Green Guide to determine the best window exposure for your plant baby as soon as you bring it home, and make sure you add an artificial light source or change its environment as soon as you notice any negative symptoms.

If your plant has experienced abnormal growth, prune it back, upgrade its conditions, and wait — in time, you might have a healthier plant.