Garlic Mustard is an invasive species that is rapidly colonizing North America. This article is to inform you on the biology of it, how to identify Garlic Mustard, and how to control Garlic Mustard.
An extremely invasive plant, it has the rare ability to spread without any form of human intervention/disturbance, and can take over pristine forest understory spaces by itself. This will reduce the natural diversity of plants that exists and crowd out the natives. In the end its impact will be detrimental for all wildlife, as many different organisms rely on the naturally occurring native species that exist in our complex ecosystem that has evolved over millennia. To read more about the importance of Native Plants, click here. I’ve been battling this plant along the forest edge in my backyard for two years. It is a long term commitment to eradicate this bad invader.
With a natural range in Europe and Western Asia, this plant was most likely introduced into North America in the 1800’s. I’ve read multiple references all stating that the plant was first noted on Long Island New York in 1868. Since it is commonly used for food in Europe, most people think it was intentionally brought over for human consumption.
Garlic Mustard Facts
Native to Eurasia in moist environments
This is a member of the mustard family of plants, as its common name would imply
Garlic Mustard has successfully invaded nearly the entire East Coast of North America, the Midwest, and Pacific Northwest
This plant is not heavily utilized by native insects or mammals/herbivores – aka nothing really eats it. Not enough to kill it off naturally, which is unfortunate.
Will completely take over a forest or shaded area. But can colonize like heck in full sun too.
Garlic Mustard is Allelopathic, meaning it produces chemicals that hinder or prevent growth of other plants. This helps the plant crowd out other native species.
The scientific name of Garlic Mustard is Alliaria petiolata
The Impact of Garlic Mustard
This plant can crowd out almost all other plants at localized sites. Nature is a complex system, and our local ecosystems have developed through trial over thousands of years to produce the species we know have. Plants that reduce this diversity and don’t benefit our native species will reduce their numbers, making our ecosystem even more fragile.
Further compounding the spread of this plant is that it is allelopathic. The plant produces a chemical that is emitted in the roots that will retard or prevent growth of other species, which is a process known as allelopathy. Reducing diversity of plants limits the food for insects and herbivores. Plants that are most affected and suffer from Garlic Mustard are herbaceous woodland wildflowers that like moist forest soils. Examples of these plants would be Virginia Bluebells, Dutchman’s Breeches, Trout Lily, and Jack in the Pulpit just to name a few.
Additionally, the chemicals emitted by this plant can negatively affect mychorrizal fungi that trees depend on for nutrient transmission.
Most animals/insects won’t eat it!
Deer, rabbits, and other herbivores don’t eat Garlic Mustard, at least not much. So, this further impacts native plant populations. If Garlic Mustard is present at a site, and the normal animals won’t eat it, that means they will consumer the other native species more heavily – to the point of freeing up space for more Garlic Mustard.
I’ve read reports of field observations that counted fewer than 12 insects visiting garlic mustard for nectar or forage. So, the presence of Garlic Mustard, by displacing native plants (that are valuable to insects), is detrimental to these insects. And so the food chain continues, in that various other birds and animals eat these insects, there will be fewer of them, and so on. This is one of the reasons why native plants are so important, and also illustrates second order effects of invasives. Remember, nature is a complex system, and small local changes can have many effects beyond that are not always obvious.
General Physical Description, Identification (more pictures below), and Life Cycle
First Year Plants
First year plants will consist of a basal rosette / cluster of leaves on the ground. The leaves at the base will be heart/kidney shaped and range in size from 2″ to 6″ diameter, and there are generally 3 or 4 leaves in the rosette. These leaves will be veined and have round serrations around the edge. Each leaf will have a stem that is 0.5″-1.5″ long. It is easy to not notice the plant at this stage, as it can just blend in with the surroundings and look inconspicuous. But it is easy to identify if you are actively looking for it.
Second Year Plants
Second year plants will also have a rosette of leaves, but will will send up a stalk that will be 1-3′ tall (typically). The leaves on the stalk will be alternate, short stemmed, saw-toothed and triangle shaped. These triangle leaves will be approximately 2″ wide at the base of the triangle. Young leaves will smell like garlic if you crush them in your hand.
Note – if you pull Garlic Mustard, but the stalk breaks or you don’t get enough of the root, the plant will send up new stems. These will then form more flowers.
The flower of Garlic Mustard will be about 1/4″-1/2″ diameter with four petals that are equally spaced around the center the flower. The petals will be 1/8″-1/4″ long. The flowers bloom in Spring just about the time when everything is starting to leaf out. After blooming, a long capsule will form containing thousands of small seeds.
Garlic Mustard has a small, shallow taproot that is easy to pull if the ground is sufficiently moist. The roots have a strong, but nasty garlic smell.
Additional Notes on ID / Life cycle
This plant will form its seeds in late May and early June. After that the plant will die, and seed capsules will open distributing the small seeds. The dead plant will remain upright throughout the year holding its seed capsules.
The new plants germinate in the Spring, and will grow throughout the year. So, make yourself familiar with the basal rosette! If you notice it, pull it.
This plant is versatile in where it can grow. It can grow in full sun, or full shade. So, just about anywhere that has temperate rainfall levels (~20″ per year) can support garlic mustard. I’ve personally observed significant colonies of this plant growing in deep dark woods with a thick canopy, carpeting the ground. It also occurs in meadows, pastures, along roads and waterways – just about anywhere if left unchecked.
How Garlic Mustard Spreads
Garlic Mustard spreads via seeds. Each Garlic Mustard plant produces thousands of seeds that are easily spread by water, human foot traffic, and wildlife. This plant has an amazing ability seemingly explode in population and blanket entire areas quickly. This plant can be self-pollinating, meaning that no insects need to visit it to give it its pollination necessary for seed production.
The seeds remain viable for about 4-5 years. So, even if you completely clear an area of Garlic Mustard, you will most likely need to return to pull more plants for several years. This is one of the main reasons that this plant is so hard to control and eradicate.
How to Control Garlic Mustard
With aggressive invasive plants, it is important for you to be aggressive too in attacking them. As soon as you see these plants, pull them before seed capsules form! But also be wary that sometimes the flower can still produce seed capsules after pulled!
Preventing Garlic Mustard from strongly establishing itself is the best means of control. If you see any plants flowering, pull them immediately. Do not compost them, burn or dispose in the trash.
Pulling up Garlic Mustard
A very effective method to control Garlic Mustard is to pull up every single plant you see, and dispose of them properly. If the plant has not flowered, or is a first year rosette, you can leave the plant on the ground to just dry out/die. If it has flowered or seed capsules are present, make sure you bag them up and dispose of them in a landfill. Alternatively you can burn the plants (following all local laws/ordinances).
The best method to pulling Garlic Mustard
Pull plants in Spring when the soil is generally moist
Grab the plant at the base, where it meets the ground. This makes it easier to get the entire root.
If the plant is flowering, burn or dispose of the plant in a trash bag. Sometimes the plant can finish flowering and make seed even if pulled early enough.
Revisit the location the following Autumn (to find basal rosettes) and next Spring to get new plants. The seeds of a plant are able to be viable for 5 or more years.
Pulling Garlic Mustard is very easy in early Spring when the ground is moist. Just go over, grab the plant, and pull it up. Must you must look at any plant you pull to make sure there are no seed capsules. You have to stay vigilant, as a single plant has the ability to produce thousands and thousands of seeds.
Pull again in Autumn
In late Summer and early Autumn, you can identify the basal rosette leaves of garlic mustard as many other plants are going dormant. Once you have learned to identify their distinct leaves, you can go patrol a site for new plants that germinated over the summer. The ground generally becomes more moist in late Summer, which makes dislodging the small taproot easy. I’ve found pulling this plant in the late Spring to be helpful in reducing the number of plants the following Spring, as I’m effectively killing everything that germinated that year.
Mowing is generally not effective at controlling Garlic Mustard. The first problem is that the small leaf cluster / basal rosette is very low to the ground, and will send up stalks later. Furthermore, if the flower stalk is mowed, the plant will just send up more stalks and bloom. An additional problem is that if seed capsules have formed, even after being weed-whacked or mowed, they can still mature from a plant that is laying on the ground. So, they will still produce seed.
For small or isolated infestations you should be probably avoid chemical control methods, as you may be killing the ‘good’ plants along with the garlic mustard. It can be difficult to keep the herbicide application only on the Garlic Mustard. However, chemical application may be the best option for areas completely covered in Garlic Mustard. But, you must apply a herbicide early in Spring, well before seed capsules develop. And, as with other methods you will likely need to return the following Spring to pull more plants since the seeds of garlic mustard are viable for about 5 years. And if the area was completely covered, you probably have a large seed bank in the area.
Just make sure you follow all instructions and local laws, ordinances as well as proper personal protection equipment!
Garlic Mustard is Edible
This plant is commonly eaten in Europe in salads and other manners. Young leaves can be eaten raw in salads or as a garnish. Roots, flowers, and leaves can be cooked in a variety of ways, be it making a sauce or general ingredient. Older, more mature plants may have too strong of a flavor.
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