By Larry Hodgson
Variegated plants are very popular in our gardens. But what is variegation? And why does it attract so much attention? That is, dear readers, the subject of the day!
A Bit of Nomenclature
Most gardeners already know the term “variegated.” It applies to something that exhibits more than one color, usually a leaf or a stem, sometimes a flower. And the state of being variegated is called “variegation.” You’ll also see a similar term—variegatum, variegatus, variegata, etc.—in many botanical names: Codiaeum variegatum for the popular houseplant, croton, with multicolored leaves, or Weigela florida ‘Variegata’ for the popular green and white variegated weigela.
If a leaf is variegated, it’s usually because it’s partially lacking in chlorophyll, the photosynthetic pigment that gives plants their normal green coloration. The part of the leaf that lacks green pigmentation allows other pigments present in the leaf, but normally masked by chlorophyll, to show through. White, cream or yellow are the usual colors, but you do occasionally see plants with pink, orange or even red variegation.
Since such a leaf is partially lacking in chlorophyll and it’s chlorophyll that, by converting sunlight into carbohydrates, gives the plant its energy, a variegated plant is often less vigorous than an all-green one. So, in nature, variegated plants rarely survive for long. We humans, however, seem to love variegation and make serious efforts to keep these variegated plants alive so we can use to decorate our flower beds, shrub borders and even homes.
How Variegation Begins
Probably well over 90% of the variegation you see in gardens is the result of a mutation. Sometimes a seedling germinates which is not green like the others, but bi- or tricolored. Or the mutation occurs on an already growing plant. A stem begins to produce bicolored leaves, and if this stem is carefully removed and multiplied, it is often possible to create a plant where all the leaves are variegated.
Sometimes this variegation is the result of an otherwise benign virus that affects the distribution of chlorophyll. In such a case, the virus can be transferred from one plant to a related plant by grafting a normal stem onto a virus-infected stem. The virus then migrates into the new stem and soon it starts to produce variegated leaves. This is best known in flowering maples and hibiscus, where almost all known variegations are of viral origin. However, it’s not a type of variegation you see very often.
Finally, there are certain plants that are naturally variegated and are found as such in the wild. Usually their variegation is symmetrical, unlike the variegation resulting from mutations or viruses that generally varies from leaf to leaf. There is actually quite a large number of naturally variegated plants and they occur in many plant families.
For example, snow-on-the-mountain (Euphorbia marginata) is a sometimes overlooked annual that produces leaves with white variegation. This is not a human selection: it grows this way in the wild too. The white markings are present on young plants but are quite discreet, then increase as the plant matures. It turns out that they serve to attract pollinators and direct them to plant’s otherwise rather inconspicuous flowers.
Other plants have markings that seem to deter predators. They can, for example, give the impression that the leaf margin or blade has already been attacked by a leaf-eating insect. This would be the case with spots found on the leaves of the polka dot plant (Hypoestes phyllostachya): to the insect’s eye, the leaf appears to be full of holes, a sign it has already been predated on. And sometimes the markings on a leaf are reminiscent of the insect’s eggs, making the leaf look like it was “already taken.”
There are also cases where the variegation seems to serve mainly as camouflage, making the entire plant less visible to predators.
That said, there are still many naturally variegated plants where botanists have yet to find a logical explanation for their usual leaf markings. Most do assume there must be one, since Mother Nature would be unlikely to develop such complex strategy if it serves no purpose!
The Advantage of Variegated Plants in the Garden
As mentioned, some naturally variegated plants turn their unusual coloring of their foliage to their advantage, but the majority of the variegated plants we grow are not genetically stable ones found in the wild, but rather cultivars (cultivated varieties) produced in nurseries … and their coloration has no genetic advantage other than appealing to gardeners!
Gardeners love them, of course, because colorful foliage plants add interest to the garden. When everything in a garden is green, even when the texture of the leaves of different plants is varied and there are various shades of green, the effect can still be a bit monotonous. But with variegated foliage adding a splash of brighter color here and there, the whole bed comes to life.
“But,” you say, “flowers too can spice up a landscape!” And you’re right. In fact, most garden enthusiasts use a large number of flowering plants in their landscaping projects. But flowers are often fleeting, fading away after just a few days or weeks, meaning you have to plan a careful mix of different plants to ensure long-term color. Colorful foliage, on the other hand, usually lasts the entire season, from spring to fall; even all year around in the case of evergreen variegated plants.
Variegated plants therefore offer the gardener the consistency that blooms can’t deliver.
And there are places where conditions aren’t that conducive to impressive bloom. Or else, such bloom simply isn’t long-lasting. That’s especially the case with shade gardens. Yes, you can have impressive spring bloom as long as sunlight still reaches through the overhanging branches barren of foliage, but when the trees leaf out, most flowers disappear. And shade plants that bloom in summer or fall tend to have fairly unimpressive or short-lived flowers.
That’s why variegated plants are most popular in shade gardens: they at least can ensure color through most of the growing season. And sometimes the white or yellow of plant variegation shines like a beacon in a shade garden that would otherwise be dark and gloomy.
As a result, many gardeners don’t hesitate to include variegated plants in their plant palette. In fact, you’ll often find beginning gardeners concentrating on blooming plants while experienced gardeners go more for leaf color.
Growing Variegated Plants
Many variegated plants that occur spontaneously from mutations lack vigor or don’t live long. These are quickly eliminated during nursery trials and don’t reach gardeners. On the other hand, some show almost as much vigor as the normal species and are no more complicated to grow. These are the varieties that can be found in nurseries.
One thing to watch out for when on a plant shopping spree, though: some variegated plants are strongly colored in spring, but that coloration fades over time, leaving a plant almost entirely green in summer. This is the case, for example, with the variegated Japanese lilacs ‘Chantilly Lace’ (Syringa reticulata ‘Chantilly Lace’) and ‘Golden Eclipse’ (S. reticulata‘Golden Eclipse’). Before you purchase a variegated plant, you might want to ask the merchant whether the color will at least last all summer!
Often, it’s the growing conditions that cause variegated plants to “green up” in summer. Nitrogen-rich fertilizers (the first of three N-P-K numbers on the label of all fertilizers) tend to have this effect. For variegated plants, therefore, a fertilizer where the first number is less than 10 is recommended. Either that, fertilize with compost, which releases its nitrogen slowly with little risk of turning the foliage green.
Beware of Reversions
Almost all variegated plants are subject to reversions, that is, branches or sections that lose their variegation and turn completely green again. Essentially, these parts have mutated back to their original coloration. If left in place, these reversions, being more vigorous than the variegated parts, tend to take up more and more space over time until they dominate the variegated part entirely. So, you should eliminate them when you see them. Just cut them out!
I’m not saying all variegated plants revert to a green form, but it’s definitely not a rare occurrence.
A Few Examples
You’ll discover variegated plants in all plant categories: trees, shrubs, conifers, perennials, annuals, houseplants, etc. It’s up to you to choose your favorites!
Here are a few examples of variegated plants to get your mouth watering.
Coleus (Coleus scutellarioides): Probably the plant with the most variegated foliage choices is the coleus. This annual (in fact, it’s a perennial in the tropics, but grown as an annual in temperate climates) offers marked, mottled bi-, tri- or even quadricolored foliage in almost every shade except true blue. Nowadays, there are hundreds of cultivars offerings different sizes, colors, habits and leaf shapes. Grow it outdoors in the summer (but remember to bring in cuttings for the winter you can maintain for next year’s garden) or as a year-round houseplant. If flowers appear at stem tips, clip them off.
Sun or shade. Dimensions: 8–36 inches × 8–12 inches (20–90 cm × 20–30 cm). Hardiness zones: 10 to 12.
Variegated Tatarian Dogwood (Cornus alba ‘Argenteo-marginata’, syn. ‘Elegantissima’): A classic garden shrub, with red stems, especially noticeable in winter, and foliage strongly variegated white. The flowers and fruits are white too, but don’t add much to the plant’s effect because the colorful foliage dominates.
Sun or shade. Dimensions: 6–10 feet × 5–10 feet (2–3 m × 1.5-3 m). Hardiness zones: 2 to 7.
Harlequin maple (Acer platanoides ‘Drummondii’): a large tree with green and white foliage. Oddly enough, this mutation of the Norway maple seems little prone to tar spot disease, a common problem with other Norway maples in many areas. Remove any reversions.
Sun or partial shade. Dimensions: 50 feet × 40 feet (15 m × 12 m). Hardiness zones: 4 to 7.
Gold-striped Hakone grass (Hakonechloa macra ‘Aureola’): a short ornamental grass forming a dome of foliage. The narrow leaves are mostly yellow with only thin green margins. Flowers are insignificant.
Sun or partial shade. Dimensions: 12–20 inches × 16–28 inches (30–50 cm × 40–70 cm). Hardiness zones: 4b to 9.
Hosta (Hosta spp.): There are literally hundreds of variegated hostas, most with margins variegated either white or yellow, but sometimes, it’s the center of the leaf that is variegated while the leaf edge that is green (or blue). You choose! But first ask the merchant if the hosta you’re eyeing is slug-resistant or not. What good comes from planting a variegated hosta if its foliage will always be full of holes?
Sun or shade. Dimensions: 6–60 inches × 6–120 inches (15–300 cm × 15–150 cm). Hardiness zones: 3 to 9.
Spotted dead-nettle (Lamium maculatum): a ground cover with abundant silver-covered foliage surrounded by only a narrow green margin. This is not a typical variegation: the silver variegation comes from tiny air bubbles just inside the leaf. There are several cultivars with pink, purple or white flowers. Great for creating a silver carpet, but watch out: it spreads!
Sun or shade. Dimensions: 8–12 inches × unlimited (20–30 cm × unlimited). Hardiness zones: 4 to 8.
Variegated plants: so much to discover!