Lemon verbena, known botanically as Aloysia citrodora, is a highly aromatic perennial shrub prized for its intense, clean lemon scent. Originating in South America, specifically Argentina and Chile, this herb is extremely popular in global culinary and cosmetic applications, from flavoring teas and desserts to creating perfumes. The maximum size this plant achieves is highly variable, depending almost entirely on the environment it is grown in and the active cultivation methods a gardener employs. A lemon verbena’s growth can range from a small, annual-sized pot plant to a substantial, permanent landscape feature.
Typical Growth Dimensions and Habit
Lemon verbena exhibits a growth habit best described as a woody, deciduous shrub. In its native, frost-free, subtropical environment, where it can establish extensive root systems over many years, the plant has the potential to become a small tree. In these ideal conditions, where it is not subject to annual dieback, Aloysia citrodora can reach impressive heights, sometimes growing up to 10 to 23 feet (about 3 to 7 meters) tall.
When grown in temperate climates, where it is treated as a tender perennial or annual, its size is significantly reduced. Most cultivated lemon verbena plants are maintained as a manageable shrub, typically reaching a height between 3 and 6 feet (about 1 to 2 meters) with a similar spread. This common size represents a balance between maximizing leaf production for harvest and keeping the plant small enough to be portable or protected during winter. The plant is deciduous, shedding its leaves in colder temperatures and revealing a woody, multi-stemmed structure.
Environmental Factors Influencing Size
The ultimate size of a lemon verbena plant is largely determined by the natural limitations of its growing location, particularly temperature and light. The plant thrives in warm, sunny conditions and is classified as a perennial only in USDA Hardiness Zones 8 through 11, where temperatures rarely fall below freezing.
Temperatures dipping below 40°F (4°C) will prompt the plant to drop its leaves and enter a dormant state, and sustained freezing temperatures can kill the plant entirely. A minimum of six to eight hours of direct, full sunlight daily is also necessary to fuel the robust growth that leads to maximum height and the highest concentration of aromatic oils in the leaves.
The composition of the soil also plays a role in facilitating larger growth, as the plant requires rich, well-draining soil with a pH that is neutral to slightly acidic. Poorly draining or heavy clay soil can lead to root rot, which inhibits the plant’s ability to absorb nutrients and water, thus stunting its development. Consistent moisture is beneficial for vigorous growth, but the roots must never be constantly waterlogged to prevent decay.
Managing Size Through Cultivation Techniques
One of the most common methods of size management is regular pruning, which encourages a fuller, more attractive shape. Frequent harvesting of the leaves for culinary or aromatic use naturally acts as a form of pruning, encouraging the plant to branch out laterally instead of focusing on vertical stem growth.
For plants that are grown in the ground and have become lanky or woody, a hard cutback by one-third to one-half of the plant’s size in the early spring coaxes new, more compact growth. This encourages a dense, bushy form that is easier to manage and yields more leaves. The timing of this pruning is important, as cutting in the fall can leave the plant vulnerable to cold damage through the open wounds.
Growing the plant in a container is the single most effective technique for permanently restricting its size. The physical constraint of the pot limits the expansion of the root system, which in turn limits the size of the above-ground foliage. Container-grown lemon verbena rarely exceeds 2 to 3 feet tall, even with multiple seasons of growth, because the plant is naturally kept somewhat pot-bound.
Bringing the potted plant indoors before temperatures drop below 40°F prevents the plant from dying back to the ground, allowing it to survive and resume growth the next season. This container strategy also directly supports the need for overwintering in colder climates, which is another size-limiting factor.