Lemon verbena

Identification and origin

Aloysia citrodora belongs to the verbena family, Verbenaceae. It is native to South America, from southern Bolivia to northwestern Argentina, and to Paraguay. It was brought to Europe in the 17th century and grown there for its essential oil, and it has since become naturalized in several warm regions. The genus honors Maria Luisa, Princess of Parma, and the species name citrodora means “lemon-scented.” It is still often sold under its older names, Aloysia triphylla and Lippia citriodora.

It is a woody, multi-stemmed shrub with an upright habit; it is deciduous but can keep its leaves in frost-free regions. In its native habitat it reaches 10–15 ft; planted in the garden it forms a clump 6–8 ft tall and wide, and in a pot it stays around 2–4 ft. Its simple, narrow, lance-shaped leaves, often arranged in threes around the stem, measure 3–6 in: they are glossy, pointed, rough to the touch and give off a strong lemon scent when crushed. The stems, by contrast, are not fragrant.

From midsummer to early fall, tiny white to pale lilac flowers open in loose clusters at the branch tips. Inconspicuous but fragrant, they are pollinated by insects.

Light

It needs full sun, meaning at least six hours of direct light a day, and tolerates light partial shade at most. The foot of a warm, sunny wall, sheltered from wind, suits it especially well; in a windy spot, stake it to keep it upright. In a container, turn the pot regularly to prevent lopsided growth. When brought indoors for winter, it needs a very bright spot.

Watering

During the growing season it needs plenty of water: keep the mix evenly moist but never soggy. Check the moisture with your finger and water as soon as the surface begins to dry, without waiting for the whole root ball to dry out. It cannot stand wet feet, so empty saucers and use a pot with drainage holes.

In the ground, moderate watering during warm months is enough once the plant is established. In fall, when the leaves drop in response to cold, water only as needed, always checking the mix before adding water: a leafless plant uses far less.

Potting mix

It prefers light, fertile, moist, well-drained soil rich in organic matter. It copes with chalky, loamy or sandy soil, whether acidic, neutral or alkaline. In clay, work in organic matter before planting to lighten the soil. In containers, use a good-quality, peat-free, loam-based potting mix in a pot that drains freely.

It is a heavy feeder: in a container, apply a general-purpose liquid fertilizer about every two weeks during the growing season, and feed less often once it is indoors. In the ground, fertilizer is unnecessary if the soil was well prepared. A thick mulch of compost or manure in fall protects the roots.

Temperature

It is frost-sensitive. In the ground it is grown in USDA zones 8a to 10b and, in coastal or mild-winter areas, withstands lows of around 23–34 °F. Cold causes leaf drop and dieback of some branches. Elsewhere, grow it in a container and bring it indoors before the first frost: losing its leaves indoors is normal. Do not move it back outside until spring, once frost is over.

Repotting

Growing it in a container limits its size and makes overwintering easier. Choose a pot with drainage holes and a loam-based mix. Over the years, older plants become very woody and their foliage thins: rather than repotting them indefinitely, take cuttings and replace the mother plant with young ones, which are more vigorous and attractive.

Pruning

Prune in early spring, as new leaves emerge: remove dead wood, thin and cut back the branches for a bushier plant. During the season, regular pinching or frequent harvesting keeps it compact and prevents legginess. To control size, a second pruning can be done from mid to late summer.

Harvesting and pruning go hand in hand: pinch the stem tips for the youngest leaves, preferably before flowering. Use the leaves fresh, or dry them at room temperature and store them in an airtight jar. They flavor teas, desserts, fruit salads, jams and sauces, and go into potpourri.

Propagation

Cuttings are the best method: seed set is unreliable, and it is better to start from a nursery plant than from seed. Take cuttings from soft shoot tips: they root easily, and the young plants grow quickly. It is also the simplest way to renew an aging plant.

Common problems

• Leaf drop in fall or indoors: a normal response to cold and the start of dormancy.
• Dead branches in spring: frost damage; wait for new growth, then remove the dead wood.
• Leggy, sparse plant: not enough pruning or pinching, or an aging plant.
• Damaged roots, decline: waterlogged soil or a pot without drainage.
• Pests: aphids, whiteflies, mealybugs and two-spotted spider mites. The plant has no serious problems.

The same symptom can have several causes: always take the season, temperature, watering and light into account before drawing conclusions.

Toxicity

Toxic to dogs, cats and horses: its essential oils can cause stomach upset and colic. The small amounts used in cooking or as a flavoring are not a concern. For people, it is an aromatic herb used in teas, cooking and perfumery. Keep pots out of reach of pets that chew on plants and contact a veterinarian if a large amount is eaten.