This plant profile shares helpful tips and tricks for growing lemon verbena.
Growing Lemon Verbena
Plants grown outside their native territory often need special care, and the South American native lemon verbena (Aloysia triphylla) is an excellent example. North American home gardeners who try to grow this tender, wonderfully fragrant perennial herb may succeed more often than they fail, but a large number who try year after year eventually develop a deep sense of frustration and guilt when they repeatedly “commit herbicide”.
Many of the latter group responded sympathetically to Linda Ligon’s editorial in the December 1991/January 1992 Herb Companion, in which she expressed frustration at her own inability to keep lemon verbena plants alive. Other readers offered constructive advice and encouragement along with their tales of radiant success. Letters of both types are included with this article, and beginning on page 54 in the hardcover copy of this issue.
A curious pattern became evident from those responses and from subsequent research and conversations with growers around the country. Many people who consistently fail in their attempts to grow lemon verbena live near people who have the opposite experience—those who fail often get their plants from those who succeed—yet neither group seems certain why one can barely coax an inch of growth from a 6-inch plant while the other cuts a 5-foot bush back to 3 feet twice in the same season.
Although our research doesn’t claim to have solved the mystery or to offer a sure-fire formula for success, it has uncovered a few misconceptions about the plant and a lot of solid advice. Those who have succeeded with lemon verbena agree that the plant is worth a bit of effort, and we hope that discouraged verbenaphiles will give it another try, armed with information and a positive outlook.
Profile of the Victim
Lemon verbena is one of more than 30 species of aromatic shrubs in the genus Aloysia (family Verbenaceae), all native to the warmer parts of North and South America. Its botanical name has undergone a cycle of change in the two centuries since it was introduced to England as Verbena triphylla. Its lemon scent was the source of an alternative name, V. citriodora (verveine citronelle in France). A Spanish researcher assigned it to the genus Aloysia (named for Maria Louisa, wife of King Charles IV of Spain) because its fruit separates into two nutlets, whereas the fruits of Verbena species separate into four. The plant was known as A. citriodora until it was moved again in the early nineteenth century, this time to the genus Lippia (named for an Italian botanist named Lippi). Though lemon verbena is sometimes still offered as L. citriodora, it has long been reassigned to the genus Aloysia, this time as A. triphylla. The species name describes the characteristic whorls of three leaves that form along the stems. Not uncommonly, however, the whorls consist of four leaves, sometimes on the entire plant and sometimes just on certain stems.
Lemon verbena grows best in loose, well-drained soil that’s rich in organic matter, and drainage is the more important of those two characteristics. Neither clay nor very acidic soils are hospitable to lemon verbena; a lot of sand and a little lime, respectively, seem to be the best remedies. Though moisture-retentive soil is often recommended, lemon verbena will rot if its roots are constantly wet.
Given adequate drainage, lemon verbena can tolerate a wide range of watering regimes. To err on the dry side seems to be most advisable, but observation and familiarity are the best tools for determining water needs. If you live in a climate colder than Zone 9 and plan to winter your lemon verbena outdoors, you should withhold water as freezing weather approaches so that the plant can harden off and so the roots will not be wet when they freeze. The plant will need little to no water while it is dormant, whether indoors or out.
Fertilize lemon verbena as you would any other herb plant: as often as every two weeks indoors or every four weeks in the garden when the plant is growing vigorously, less during periods of slower growth, and not at all during dormancy. In spring, following winter dormancy, some gardeners apply fish emulsion or other fertilizer to encourage growth to begin, but others question whether it’s the fertilizer or just the water that stimulates the process.
In more northern regions, lemon verbena thrives in full sun; even better is a site in the reflected light of a white fence or greenhouse wall. Closer to its native latitude near the equator, it grows better with at least some shade during part of the day.
Cultivated lemon verbena flowers and sets its two-seeded fruit most dependably in southern zones where the growing season is long, or in the more northern zones under lights. Flowering apparently depends not only on the length of the growing season, but also on stem length, and gardeners who tend to prune lemon verbena fairly hard probably will not see many flowers. The blossoms are small, numerous, and white to pale purple, clustered along the last few inches of the main stem and on short stems in the leaf axils.
For many herbs, pruning stimulates the emergence of new growth at several points along the remaining stem, but lemon verbena responds mainly at the whorl of leaves immediately below the cut. This habit gives the topiary gardener quite a bit of control, but it also means that frequent, severe pruning is required to keep the plant from becoming inordinately leggy and to increase foliage production (not to mention keeping the drying racks full).
An Herb That is Leafless, But Not Lifeless
Almost without exception, gardeners growing lemon verbena for the first time are dismayed when the plant drops all its leaves, which this herb does with the slightest provocation. The leafless sticks look so pitiful that many gardeners, thinking that the plant has died, toss it onto the compost pile. Some later have discovered the “dead” plant growing vigorously where it was thrown.
Although lemon verbena often loses its leaves and becomes dormant when days become short, it grows year round in its native haunts, where day length is virtually unchanging, and dormancy does not seem to be a requirement for its health and longevity. When temperatures fall significantly below freezing, the leaves often are damaged and eventually fall off. Some sources indicate that freezing temperatures alone can trigger dormancy, but Tom DeBaggio of Arlington, Virginia, has found that a frozen plant that is brought indoors and placed under lights to simulate summer day length will continue to produce new growth after the damaged leaves have dropped off. His experience has convinced him that day length is the main factor that triggers the metabolic slowdown of dormancy.
In plants that are wintered indoors, sudden leaf loss frequently appears to be a reaction to rapid temperature change or root disturbance. It can be triggered by bringing a potted plant indoors in late summer or after the first frost, by digging up a plant from its summer garden spot and potting it for indoor winter growing, by transplanting a small plant into a larger pot, or simply in response to a strong, cold draft.
Many gardeners grow lemon verbena in a pot so that it will be easy to move indoors and out as the weather dictates. This is convenient and avoids annual transplant shock, but a pot differs from the ground in that the soil inside the pot changes temperature much more quickly—another source of shock. Choose a pot at least 12 inches in diameter to allow the roots ample growing room and to limit the effect of short-term air-temperature changes on soil temperature. This effect can be decreased further during the plant’s outdoor sojourn by burying the pot in the garden. The risk in this strategy, however, is that the roots may grow out the drainage holes in the pot and be broken when the plant is exhumed in early fall. Such root breakage can retard growth significantly and will probably cause leaf loss. It may be helpful to cut such plants back a little to accommodate the loss of roots.
Cold Hardiness of Lemon Verbena
Different sources list different temperatures—from 14 degrees to 22 degrees Fahrenheit—below which lemon verbena is not likely to survive. However, Andy Van Hevelingen of Newberg, Oregon, had an uncovered lemon verbena that survived a single night at 3 degrees Fahrenheit. Conditions were optimal: the stems were protected from wind, the soil completely dry around the roots, and the decrease in temperature gradual over a few weeks so that the plant had time to harden off and become fully dormant. Protection from wind seems to be critical near the edge of the plant’s hardiness range; try wrapping the dormant top with weatherproof plastic foam or burlap or covering it with mulch. Kae Snow-Stephens of Shreveport, Louisiana, covers the small but actively growing lemon verbenas in her garden with plastic garbage bags when the cold becomes threatening, and they have not only survived one-night temperatures as low as 22 degrees Fahrenheit, but have done so without losing leaves or slowing their growth.
For some gardeners, lemon verbena that winters outdoors is one of the first plants to emerge from dormancy, but others in similar climates report that growth resumes later in lemon verbena than in other perennials. If spring has sprung and you’re wondering whether your lemon verbena will ever come back, you can test for signs of life by bending or clipping off the ends of the dormant woody stems. Dry, brittle wood is dead, but you may find that the stems are alive closer to the base of the plant. One experienced gardener recommends that you resist the temptation to perform such a test because the dead wood protects that which is alive; if your curiosity can survive the wait, the answer will come eventually in the form of new growth (or its continued absence).
Dealing With Lemon Verbena Leaf Loss and Dormancy
Like other plants, lemon verbena transpires or gives off water mostly through its leaves, and it stands to reason that a leafless plant uses far less water than one covered with leaves. One of the common ways gardeners kill lemon verbena is by overwatering during leafless periods; this is especially easy to do if you’ve been watering on a time schedule. Whatever the immediate cause of leaf loss, watering must be cut back drastically, preferably by reducing the frequency of watering rather than by applying smaller amounts on the same time schedule.
In the northern United States, where lemon verbena is sure to succumb to winter cold outdoors, many gardeners allow the plant to endure early frosts, then bring the leafless plant inside and put it in a cool, dark place to rest for the winter. During this period of indoor dormancy, it receives little or no water. In early spring, the plant is watered, occasionally fertilized, and placed in a warm, sunny spot; growth should begin within a couple of weeks.
Lemon Verbena Propagation
If your lemon verbena does flower, the chances of obtaining viable seed are marginal, so lemon verbena is usually propagated vegetatively. Those who grow this plant successfully advise taking basal cuttings of the current year’s growth in summer when the plant is growing vigorously. Such cuttings root fairly easily (see “Growing Herbs from Stem Cuttings” in the February/March 1993 Herb Companion). If taken in early fall or later, when growth slows as the days shorten, cuttings will take longer to root (which increases the chance of failure) and are less likely to survive transplanting. If you do take cuttings late in the growing season, root them in 2 1/2- or 3-inch pots to postpone the need to disturb the new root systems, and use supplemental lighting, if possible.
Lemon Verbena Pests
Lemon verbena is a favored delicacy of whitefly and spider mites; many experienced gardeners and commercial growers refuse to have this herb around because they feel it attracts those pests. However, an equal number—many in the same climates—either experience no such problems or find the pests easy to deal with. Home gardeners with just a few plants can combat an infestation of whitefly or spider mites by spraying the leaves top and bottom with insecticidal soap, or with a solution of dishwashing liquid (1 teaspoon), vegetable oil (1 tablespoon), and water (1 quart) three times at ten-day intervals, rinsing about three hours after application. Indoor plants should be isolated from other house plants during treatment. Misting the plants thoroughly at least twice a week after treatment is said to discourage mites from recolonizing.
Why We Keep Trying to Grow Lemon Verbena
The charm of lemon verbena is apparent to anyone who encounters it. It can be a neat bush if kept tightly groomed, or its stems can extend into quite a sprawl. The leaves are a cheery shade of light green. But the great joy of lemon verbena is the sweet, lemony scent that leaps from the leaves at the slightest touch. This fragrance is especially strong at the peak of growth in mid- to late summer.
The most common home use of the herb is in potpourri; the dried leaves can retain their scent for years, and they are commonly available, whole or powdered, from suppliers of potpourri ingredients. Tea made from the dried leaves is a delicious lemony beverage, thought by some to be the best of the lemon-herb teas. In cooking, however, lemon verbena is deceptive; insofar as smell and taste can be separated, the smell is lemony but the taste is bitter and hot, more like citrus zest than like the fruit.
The essential oil retains the delightful lemon scent that’s characteristic of the leaves, and the oil is sometimes used commercially in flavoring liqueurs. However, it is difficult to distinguish between lemon verbena and lemongrass essential oils. Lemon oil (pressed from the lemon zest) and the essential oils of lemongrass and lemon balm seem to have cornered the retail market for lemon scent and flavor; most suppliers of herbal products do not offer lemon verbena essential oil.
The herb is rarely mentioned in literature on medicinal plants, perhaps because its medicinal effects are quite mild and can be obtained more easily with other herbs. The pleasant, fragrant tea is said to act as a gentle sedative and has been used in reducing fever, settling stomach upset and intestinal spasms, and soothing bronchial and nasal congestion.
Lemon Verbena Sources
• Cricket Hill Herb Farm, Dept. H, Glen Street, Rowley, MA 01969. Catalog $1.
• Havasu Hills Herb Farm, Dept. HC, 20150-A Rough & Ready Trail, Sonora, CA 95370. Catalog $1.
• Lily of the Valley Herb Farm, 3969 Fox Ave., Minerva, OH 44657. Plant list and product list, $1 each refundable.
• Logee’s Greenhouses, Dept. HC, 141 North Street, Danielson, CT 06239. Catalog $3 refundable.
• McCrory’s Sunny Hill Herb Farm, Dept. HC, 35152 LaPlace Ct., Eustis, FL 32726. Catalog $.50 refundable.
• Rasland Farm, Dept. HC, Route 1, Box 65C, Godwin, NC 28344. Catalog $2.50.
David Merrill, managing editor of The Herb Companion, has never yet killed a lemon verbena plant.
Group Therapy for Lemon Verbena Addicts
Mail is still trickling in in response to Linda Ligon’s editorial in our December 1991/January 1992 issue. Lemon verbena clearly is important enough to warrant the stoic persistence of many gardeners, and why others nearby can grow it with no difficulty is a mystery we have yet to solve. Perhaps the answers lie in the personal accounts of both kinds of gardeners in many areas of the country. Below is a sampling of what we’ve received.
Tales of Failure . . .
I, too, am guilty of committing herbicide on more poor, unsuspecting lemon verbenas than I care to count. I can’t understand why. I buy a 3-inch plant in spring, set it in the herb garden full of wonderful expectations, water it, watch over it lovingly, but in September I still have a 3-inch plant. (Well, maybe 3 1/2 inches.) But, as always, I will return to the scene of the crime again this spring with my lemon verbena babies. Maybe this year . . .
—Ronny Kosempel, Cheltenham, PA
I stare disappointedly at the huge pot that I bought last spring, anticipating the needs of the tiny lemon verbena that I had purchased. I’ve yet to keep one of these plants alive. Our summer temperatures range into the 90s and sometimes to 100 degrees. Hope springs eternal; I’m keeping the pot and eyeing another lemon verbena plant.
—Cue Camak, Anderson, SC
If I just look at a lemon verbena, it dies—I’ve killed three of them so far. Yet an herby acquaintance right here in town has a lemon verbena bush the size of a Volkswagen, which she tends by casually slashing it back as she walks by it. I can see no logic to this.
—Robbie Cranch, Fresno, CA
I don’t want to discuss the lemon verbenas that have come into my hands to meet their demise. Herbicide is an awful thing to commit regularly on innocent plants. I always think, “It just has to live this time. I’m due!” This spring I’ll try one more time, like I always do. I’ve got to have just one.
—Cathy Leatherwood, Dallas, TX
. . . And Tales of Herb Growing Success
Last spring, I brought home a lemon verbena and planted it directly into the garden. In September, I potted it up and introduced it to its winter home in the south-facing school classroom where I teach. The first day, the leaves shriveled and died, and the kids laughed. The second day, I cut the pathetic stem to about 12 inches. And then we waited . . . and waited . . . and waited. By the beginning of December, the plant sprouted everywhere. The once-straggly stick will be a full, vibrant bush when it returns home for summer vacation.
—Eileen Gunning, Pleasantville, NY
I have five plants that I got in 2 1/2-inch pots that are now 4 feet tall. Since they must be moved in for winter, I keep them all in pots with standard potting soil, and I keep the pot significantly larger than the plant so it’s not rootbound in winter when it’s cold.
I leave the plants out through a couple of light frosts; this seems to nip any whiteflies or other bugs. The leaves also get nipped, so I prune them all off, which also eliminates possible bugs. (I’ve tried leaving the leaves on, but they fall off with the cold anyway.) I move the leafless plants into a cold frame, where they don’t get below 15 degrees. For me this seems the critical temperature; any colder, and I start getting casualties.
I water only when bone dry. We have so much rain and high humidity here that the soil is prone to mold if not completely dry between waterings. My plants begin to leaf out in February when it’s still too cold to move them outside. I water them a little more often to support the growth, but still tend to keep them on the dry side.
I’ve experimented with moving some plants outside when light frosts (around 30 degrees) are still expected, and keeping some inside until it’s warmer out. Although neither method has killed any plants, the ones that go out earlier tend to get dark green faster and are more bug-free.
I water them daily in warm weather. If they get too dry, they get brown, crusty leaves. I only feed them once or twice during the summer, and never in winter.
—Janice Keck, Tacoma, WA
I think my lemon verbena likes to be boxed in. When I lived in southern California, it grew in back of the house in a little 5-by-9-foot patch of ground between the tool shed and the extended back bedroom. From June to October, I top-sprayed it just about every day—I believe plants like to have their faces cleansed just as we humans do. Toward the end of October, I cut most of the branches, stripping the leaves for tea or potpourri.
Now that I live in the “Gold Country”, it grows against the east wall of the house with the daylilies, facing the morning sun. I’ve changed my annual routine: I wait until the last possible minute to dig it up, which is about the beginning of November (unless it snows). I put it in a 12- or 16-inch pot and give it a warm place in an upstairs bedroom. At least once a week, I give it about 1 1/2 quarts of water, and I mist the leaves frequently. One year it lost all its leaves, but they came back. Last year, it kept its leaves most of the winter.
About May, I gradually acclimatize it on the covered porch outside for about two weeks. Then it goes back out in its usual spot against the house.
—Marge Cloteworthy, Nevada City, CA
My two giant specimens (over 5 feet) have been around for at least seven years. I do recall whiteflies invading them many years ago. I’m fairly sure that I sprayed them with Safer’s soap a couple of times, and it helped but did not eliminate the pests. The next year I decided to isolate the lemon verbena from the other plants I brought in from the garden. I put it in the family room near an east-facing window, and it flourished there and flooded the room with fragrance every time anyone brushed against it. I remember cutting it back hard—to about 4 inches from the soil—sometime in February. By the following fall, that same plant and a second one had become too large to be house plants.
Now I bring them into a dimly lit, unheated entryway in the largest plastic pot available. I cut back all stems immediately to 6 to 8 inches from the soil, and then neglect them until February, watering them only lightly once a month or less. There’s nothing for whiteflies to feed on, and I haven’t had that problem recently with any of the plants I bring in.
Around the middle of February, I move them closer to the sunlight from the west-facing window in that same entryway, and start a heavier watering program. I add kelp to the water and water deeply—until it seeps from the bottom of the pot. It takes about three weeks for some green to poke through, at first at the ends of the branches. I’m elated when those first green tips appear, long before there’s any other sign of spring’s renewing power outside.
As the green tips spread all over the plant, I increase the amount and frequency of the fishy water the plants receive. By April, the green growth is getting leggy, and I clip the stems back to encourage branching.
My recommendations are: grow your lemon verbena in full sun outside all summer to make a strong plant. Treat it like a xeric plant by not giving it too much moisture. Bring it indoors in fall and isolate it from other plants that attract whiteflies. Give it near-drought conditions inside.
As with most other plants, there are probably as many ways to grow lemon verbena as there are growers.
—Portia Meares, Wolftown, VA