Alliaria petiolata, colloquially known as garlic mustard is a herbaceous biennial plant known for the garlic aroma and smell of its crushed leaves. It can be found in partially shaded and moist places like woodland edges, trails, hedges, and roadsides. Leaves of garlic mustard are used in European cuisine as a spice herb for salads and sauces.
I. Appearance and CharacteristicsÂ
Alliaria petiolata, or garlic mustard, is a biennial flowering plant in the mustard family (Brassicaceae). It is native to Europe, western and central Asia, north-western Africa, Morocco, Iberia and the British Isles, north to northern Scandinavia, and east to northern Pakistan and Xinjiang in western China.
Plants are often found growing along the margins of hedges, giving rise to the old British folk name of jack-by-the-hedge. Other common names include: garlic mustard, garlic root, hedge garlic, sauce-alone, jack-in-the-bush, penny hedge and poor man’s mustard. The genus name Alliaria, “resembling Allium”, refers to the garlic-like odour of the crushed foliage. All parts of the plant, including the roots, have this smell.
It is an herbaceous biennial plant growing from a deeply growing, thin, whitish taproot scented like horseradish. In their first years, plants are rosettes of green leaves close to the ground; these rosettes remain green through the winter and develop into mature flowering plants the following spring.
Second-year plants often grow from 30–100 cm (12–39 in) tall, rarely to 130 cm (51 in) tall. The leaves are stalked, triangular through heart shaped, 10–15 cm (3.9–5.9 in) long (of which about half being the petiole) and 5–9 cm (2.0–3.5 in) broad, with coarsely toothed margins. The flowers are produced in spring and summer in small clusters. Each small flower has four white petals 4–8 mm (0.2–0.3 in) long and 2–3 mm (0.08–0.12 in) broad, arranged in a cross shape.
The fruit is an erect, slender, four-sided capsule 4–5.5 cm (1.6–2.2 in) long, called a silique, green maturing to pale grey brown, containing two rows of small shiny black seeds which are released when a silique splits open. A single plant can produce hundreds of seeds, which often scatter several meters from the parent plant.
Depending upon conditions, garlic mustard flowers either self-fertilize or are cross-pollinated by a variety of insects.
Sixty-nine insect herbivores and seven fungi are associated with garlic mustard in Europe. The most important groups of natural enemies associated with garlic mustard were weevils (particularly the genus Ceutorhynchus), leaf beetles, butterflies, and moths, including the larvae of some moth species such as the garden carpet moth. The small white flowers have a rather unpleasant aroma which attracts midges and hoverflies, although the flowers usually pollinate themselves. In June the pale green caterpillar of the orange tip butterfly (Anthocharis cardamines) can be found feeding on the long green seed-pods from which it can hardly be distinguished.
Garlic mustard was introduced to North America by European settlers in the 1800s for culinary and medicinal purposes. The species was recorded as being in Long Island in 1868. It has since spread all over North America, apart from the far south of the US and some prairie states and Canadian provinces. It is toxic or unpalatable to many native herbivores, as well as to some native Lepidoptera.
II. How to Grow and Care
Sunlight
Garlic mustard thrives in conditions of partial sun where it can receive dappled sunlight throughout the day. While it can endure full sun and full shade, garlic mustard’s growth and health are optimized under moderate light intensity. In excessive sunlight, garlic mustard may exhibit stress signs such as wilting or faded leaf color. Conversely, in deep shade, it may experience reduced vigor and sparse flowering.
Adaptive to a range of luminosity, garlic mustard adjusts its leaf orientation and pigmentation to maximize light absorption. Ideally planted outdoors, garlic mustard is best situated under the canopy of taller vegetation, ensuring a balance of light and shade.
Watering
Originating from the understory of woodlands, garlic mustard thrives in moist but well-drained soil, reflecting its adaptation to environments with moderate water availability. It exhibits a preference for consistent moisture without being waterlogged, maintaining a balance that is neither too dry nor overly saturated. For optimal growth, garlic mustard requires watering every week.
As an herbaceous biennial commonly grown outdoors, garlic mustard’s growth cycle is closely tied to water availability, with peak vegetative growth occurring during periods of ample rainfall.
Propagation
The ideal propagation season for garlic mustard is Spring, using the preferred method of sowing. Garlic mustard has a relatively easy propagation difficulty, and success can be determined by observing signs like seed germination and vigorous growth. Ensure adequate soil moisture during germination.
Transplanting
The perfect time to transplant garlic mustard is during its blooming period, from mid-spring to early summer. Choose a partially shaded location for optimal growth. When transplanting, ensure the soil is well-drained and fertile.
III. Uses and BenefitsÂ
Garlic mustard is one of the oldest spices used in Europe. Phytoliths in pottery of the Ertebølle and Funnelneck-Beaker culture in north-eastern Germany and Denmark, dating to 4100–3750 BCE, indicate its use in that era.
In 17th-century Britain, it was recommended as a flavoring for salt fish. It can also be made into a sauce for eating with roast lamb or salad. Early European settlers brought the herb to the New World to use as a garlic-type flavoring. Its traditional medicinal purposes include use as a diuretic. The herb was also planted as a form of erosion control.
Today, the chopped leaves are used for flavoring in salads and sauces such as pesto, and sometimes the flowers and fruit are included as well. The leaves, best when young, taste of both garlic and mustard. The seeds are sometimes used in France to season food. Garlic mustard was once used medicinally as a disinfectant or diuretic, and was sometimes used to treat wounds.
IV. How to Control
The plant is classified as an invasive species in North America. Since being brought to the United States by settlers, it has naturalized and expanded its range to include most of the Northeast and Midwest, as well as south-eastern Canada. It is one of the few invasive herbaceous species able to dominate the understory of North American forests and has thus reduced the biodiversity of many areas.
Because this plant is so difficult to eradicate once it is established, familiarize yourself with the flower, the plant and the habitat where it grows to find infestations early. Monitor sites regularly to remove plants prior to seed set.
- Hand-pulling
Hand-pulling individual plants is effective if the entire root is removed. Flowering or seeding plants must be put in a bag and discarded in the garbage. Carefully and thoroughly clean off boots, clothes and tools before leaving the area to avoid carrying the tiny seeds to new sites.
- Chemical Control
Herbicide may be needed for large, dense infestations and should be applied in the spring or fall on seedlings and rosettes, with care taken to avoid native and other desirable plants. Follow the product label and all laws and regulations regarding herbicide use on the site. Contact your local noxious weed program or county extension office for recommendations on herbicides.
- Follow Up
After pulling or spraying dense infestations of garlic mustard, it can help to cover the bare areas with wood chip mulch to reduce seed germination. Infested sites should be carefully monitored every year for new plants, and checked for at least three or four years after no more plants have been found to ensure the population has been eradicated.
