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Caring for variegated plants

Q: Is it true that variegated plants grow at a slower rate than plants that are all green? What about plants with yellow or red leaves?

Elijah Pickett, Fayetteville, AR

Variegated yucca. Variegated yucca. Photo/Illustration: Allison Starcher

A: Mark C. Starrett, associate professor of horticulture at the University of Vermont, responds: Yes, it is true that variegated plants grow at a slower rate. Because varie­gated plants do not have as much chlorophyll as plants with solid green leaves, they do not produce as much energy for plant growth.

The variegated part of a plant is typically the result of a genetic mutation that prevents cells in the white or yellow section of the leaf from producing chlorophyll. Without chlorophyll, the cells cannot convert sunlight energy into sugars (by the process of photo­synthesis), which the plant uses to produce new growth. Thus, the plant grows more slowly than a plant that has solid green leaves and more chlorophyll. Similarly, a plant with all-yellow foliage has sig­nificantly less chlorophyll than a plant of the same species with solid green foliage. Therefore, yellow-foliaged plants often grow more slowly as well.

You don’t want to overfertilize variegated or yellow-foliaged plants. They do not need extra nitrogen as they cannot use it. The fertilizer will be wasted and may actually accumulate around the roots of the plant, depending on soil type. When this occurs, the fertilizer (which is a salt) prevents water uptake by the roots, causing the foliage to desiccate, which will appear as browning.

In addition to providing energy, chlorophyll protects plants from sunlight. In a variegated or yellow-foliaged plant, if there isn’t enough chlorophyll in the leaves to absorb all of the sunlight energy, then the foliage can “burn.” This creates a tricky situation. Often variegated plants do well in an area where they get some sunlight because it provides the plant with enough energy to survive and grow. However, if they are given too much sunlight (especially in warmer parts of the country), variegated leaves or yellow foliage can be damaged by the excess energy that cannot be absorbed. If your variegated or yellow-foliaged plant develops brown patches, help shade it from the warm and intense afternoon sunlight by either moving the plant to a new location or growing another plant nearby.

Red- or purple-foliaged plants are rarer. Red pigments are typically the by-product of excess sugars from photosynthesis building up in the foliage due to ample sun and active chlorophyll. The sugars made by the chlorophyll during the day provide the plant with energy at night when it is not making sugars (no sunlight, no sugars). How­ever, if the plant makes more sugars during the day than it can use even at night, it has to put them somewhere. So some plants convert the excess sugars into pigments that turn the foliage red. You may wonder why this active chlorophyll does not make these plants grow faster. The answer to that mystery comes down to plant genetics. Certain plants can process sugars faster than others and thus grow faster, while others cannot.

From Fine Gardening 101, pp. 20