Dr. Lew Feldman, Garden Director

Changing the Location of a Plant

One of the more common and challenging activities for both indoor and outdoor gardeners is changing the location of a plant, which is sometimes necessary when a plant has become too large for a particular location, or, for indoor houseplants, perhaps associated with rearranging the layout of a room. And while moving a plant might seem like a fairly straightforward task, such activity is often stressful for the plant, and sometimes, even fatal.

Often these relocations are accompanied by changes in the lighting, resulting in the plants being exposed to different (lower or higher) light intensities. In order to understand and appreciate why adapting to a different level of illumination can be formidable for a plant, we need to be reminded that a plant makes its living, its food, by capturing sunlight and using it to convert atmospheric carbon dioxide into sugars and other energy-rich compounds (this process is called photosynthesis).

Just like us, plants need a readily available supply of energy to survive.

Leaf size, thickness and shape differ on oak trees depending on whether the leaf develops in the sun or the shade charlikerns.wordpress.com

At night, when there is no light, photosynthesis does not occur, yet the plant still needs energy. The process of making and then consuming energy-rich compounds allows the plant to grow. However, a plant grows only if the amount of energy-rich compounds made via photosynthesis exceeds the amount of energy needed to keep the plant alive.

The point at which the manufacturing and loss of energy-rich compounds balance each other is called the compensation point. In most plants, in order for there to be available sufficient energy for growth, the amount of energy-rich compounds made must exceed the amount used by the plant. Each plant, therefore, depending upon its environment, establishes its own compensation point. In bright light, where the formation of energy-rich compounds is highly favored, the amount of energy-rich compounds used by the plant can also be high, allowing the plant to take advantage of the abundance of light and to grow extensively.

So what does the compensation point have to do with success (or failure) in moving a plant? Let’s begin with the situation in which a plant is growing in bright light and then is moved to a shady environment. Leaves originally produced in the bright light have established a particular compensation point that is related to the amount of photosynthesis. Suddenly moving a plant to shade now results in an immediate reduction in the production of energy-rich compounds, but without a corresponding, immediate reduction in the use of energy-rich compounds. In this situation the plant is using up its energy-rich compounds faster than it is making them. The result is that leaves are eventually starved of energy and they often fall off and the whole plant frequently dies.

Now let’s look at the reverse situation; moving a plant from a dimly lighted room to one with bright light. In locations with reduced illumination the plant has had to adapt to gathering what limited light is available. It does this by making large, often thin leaves with increased surface area for capturing the light.

Damaged leaves on an orchid plant moved from shade to more intense sunlight

Also, importantly, the leaves in the shade do not have any “filters” (usually other pigments) which function as sunscreens for reducing the intensity of the light; in shade, these leaves want all the light they can get, so they do not develop sunscreens.

Under these circumstances, moving a plant from the shade into the sunlight essentially overwhelms the photosynthesis light capture system, equivalent to getting a sunburn, and usually results in damage to the photosynthesis machinery. As a consequence, such leaves typically die.

So, is it possible to successfully move a plant into an environment with a light intensity differing from where the plant was originally located?

Yes! If done gradually. Moving plants from bright light to shade can be successful if this is done gradually, thereby allowing the already-existing leaves to slowly shift their compensation points. However, moving a plant from shade to bright light is difficult, since existing leaves cannot change their size nor thickness and usually lack the necessary sunscreen filters (= suntan lotion) for moderating light intensity.

In general, you have more success in relocating a plant if it is healthy before the move, and if you don’t mind the loss of the leaves that were present at the time of the move. The production of new leaves, with new compensation points, is generally what favors success in relocating a plant.

So on your next visit to the UC Botanical Garden, look for plants growing in both shade and sun and see if you can notice differences in the features of the leaves in these two dissimilarly illuminated environments.

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