Garlic Mustard

Garlic Mustard (Alliaria petiolata / Alliaria officinalis)

Alliaria is the genus name referring to mustard, broccoli
and other species with four-petaled flowers.

Alliaria petiolata and Alliaria officinalis are synonyms.

Photo: Le-thuy Do

This particular weed name, petiolata, refers to the petiolate-type leaf stem. This is where we get Alliaria petiolata, or mustard-leaf.

So what is Alliaria officinalis? It's just a synonym.

If one is new to gardening this weed seems appealing because it not only looks nice, it is used for medicinal purposes. The leaves, flowers and seeds are all edible along with high in vitamins A and C. If that's not enough - eat a lot of it you have a free laxative!

That's the good, now for the bad - which outweighs the good.

This is a cool season biennial. Depending on geographic location garlic mustard can behave like a winter annual or like a perennial. It seeds rapidly and becomes very invasive.
It grows practically anywhere all over the world if suitable conditions are right. It is rarely found on peat or swampy soils.
It grows in well-fertilized sites but can establish itself in poor, dry soils including sandy, loamy and clay. It can grow on limestone and sandstone underlying substrates and can even be spotted growing high up in trees.
It can grow in sunlight but thrives in shady areas like the edges of woods, trails and streams. It can also be found at the side of the road.
In North America it has no known natural enemies, is self-fertile, and produces a chemical that will prohibit other vegetation to grow around it.

This weed is mounding with heart shaped leaves having toothed edges. The flower cluster is made up of small white 4-petaled flowers.

Seed pods explode and scatter black seeds about mid-summer. If crushed, seeds smell like garlic or broccoli, depending on your nose.

Photo: Kathryn Hewitt

In it's first year seeds germinate from late February to mid-May. June into fall is the young, or Basal, stage where leafy rosettes begin to form. It runs low to the ground and begins to cluster. Clusters are dark green in color and leaves are kidney-shaped growing up to 4 inches wide.

Garlic mustard is found predominately in the eastern United States. In some areas the young weed can remain dormant over winter, whereas in other winter areas the weed leaves have the ability to photosynthesize all winter long, giving it a competitive advantage over most native species.

In it's second year surviving rosettes produce hairy leaf stalks that are erect with flowering stems. This happens in March for most areas. Growth is fast and stems grow up to 3 feet. The basal kidney-shaped leaves become more heart, or triangular-shaped as the plant matures.

From early April to early June, depending upon location is when flowering begins. Seeds are produced in pods and capable of self-pollination before flowers open. Cross-pollination occurs especially when weeds are wet and/or stick together. Seed pods are short, narrow and stand upright and ripen in mid June and pollinate through September.

Don't introduce garlic mustard to your garden or yard. Seeds can remain dormant for years. If introduced, the best management should be to focus on preventing seed from germinating.

If this weed is pulled, it is best to do in the young stages in fall where roots are not established. The second best time to pull would be in spring before the weed really starts to shoot up. Once the thin, white taproot grows deeper, it becomes more difficult to pull and seeds are very likely to scatter.
Propane torch methods can be either successful or not. The seeds can be resilient and difficult to heat. Even more interesting, garlic mustard can come back stronger after torching because area is left exposed. Seeds grow in all kinds of soils, including 'disturbed' one's.
Any pre-emergent herbicide should be used in early spring, throughout summer when seed are germinating.
The best manual approach is to hoe, cut or mow low to the ground and focus on killing roots. Use a post-emergent, such as a glyphosate, and repeat until weed dies away. Continue to apply mulch throughout.
Depending on the location of weed, after removal place smother crop in its place. Smother crops can also be called a cover crop. A cover crop consists of certain plants that are grown over an area specifically to choke out weed growth.

FYI:

Although Garlic mustard is palatable to humans and livestock, it can be harmful to some insects, including some butterfly species.

The Pieridae butterfly family often use the Brassicaceae family (mustard/cabbage) as host plants. It has been noted that the Green Veined White (Pieris napi oleracea) and the rare West Virginia White Butterfly (P. virginiensis) females deposit eggs on garlic mustard instead of their native host plants. Many, if not all, of the larvae die before completing development. Sadly, the populations are declining for these butterflies because of this exotic Brassicaceae family weed.
Young, just emerging mustard plants are often confused with Violets (Viola sp.) and White Avens (Geum canadense).

Related Articles:

Organic Mulch Types - Options for mulches once weed is eradicated.

Exotic - Butterflies or plants, exotic does not mean it's good.

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