At a Glance
- Scientific name: Alliaria petiolata
- Annual, perennial, or biennial: Biennial – Needs two growing seasons to produce seed.
- Conditions it likes best: Shade or mixed sun and shade
- How it spreads: Makes a lot of small seeds that can survive several years in the soil before sprouting. Running water (streams or rainwater) can move seeds to new places. People can also move seeds in their boots or tires.
- How it causes damage: Makes dense patches that take over forested areas and takes the place of other plants. Prevents new trees from growing up. Studies from other parts of the United States suggest that garlic mustard roots may produce a chemical that kills some important kinds of soil fungus that tree seedlings need.
- Oregon Department of Agriculture noxious weed rank: B
- Report patches of this plant? Yes. Please report sightings of this plant to Environmental Services. Find contact information on this page. A photo and location are required.
How to Identify Garlic Mustard
Winter: Rosette. Garlic mustard looks like many other plants, including several kinds of other mustard plants. For many people, its crushed leaves and roots smell like garlic. Mustards are known for having unexpected sizes and for flowering at unexpected times, so the tips listed below may not always describe what happens in the world.
Garlic mustard overwinters as a rosette (flat circle of leaves) with round leaves with scalloped, almost toothed edges. Rosettes are easily confused with several native species (see the look-alikes section below) and can be hard to find under fallen leaves during winter.
Spring. When days get longer and warmer in April, rosettes bolt (grow a stem). Stems are usually 1-4 feet tall, and new leaves change from round to triangular. Plants as short as 1 inch or as tall as 6 feet are not unusual.
In April and May, the bolting plants will open into four-petaled white flowers. Flowers usually last two to three weeks, falling off from the top of the plant to the bottom.
Summer. By late May or early June, all the flowers have been replaced with tiny seedpods. The seedpods need one to two weeks before seeds become viable (able to create a new plant). Seeds then ripen for another four to six weeks, until the seedpods dry out and turn brown. This happens in late June or early July.
Dry seedpods explode at the slightest touch, scattering seeds all around. When this happens, well-meaning people who are pulling plants can accidentally get seeds in their clothes or shoes and then move seed to unexpected places. For this reason, we don't recommend pulling plants between late June and late October. It is better to have seeds fall where you know they are than for the seeds to go someplace you’re not looking.
Summer and Fall: Seeds Ripe. By October or November, most seeds have been knocked off the plants. Fall and winter are a good time to dig up rosettes but be sure to clean the mud out of your boots. Fall and winter are also good times to accidentally move seed around!
How and When to Remove Garlic Mustard
- Manual. Digging up garlic mustard on private property can be effective but requires weekly attention to catch new plants. Pulled plants will continue to flower and set seed. Be sure to bag pulled plants and put them in the garbage (not in your yard debris). Be sure to get all the roots. Don't cut or mow. Leftover roots can regrow, and cut plants might still flower and set seed. It is better not to pull garlic mustard on roadsides unless you have “adopted” that roadside.
- Herbicide. Herbicide treatment is not necessary on small, local patches. The City of Portland uses herbicide mostly along roadsides, where miles of work makes handpulling difficult and dangerous.
- Check. Monitor the site every two weeks in spring and especially in the second and third year after treatment when surviving seed takes its big opportunity to sprout.
- Replant. After a year or two of managing this plant, consider planting native or less aggressive non-native plants.
City Assistance and Current Work
If you’ve got garlic mustard on your Portland property and there’s too much to pull, let us know. We may be able to help. Our treatment seasons runs May to June. If the treatment season has ended, we will add your name to our treatment inventory for the following spring.
How to get assistance. Before the end of April, download and send to the Environmental Services Early Detection and Rapid Response team a completed Permit of Entry form (link below). Contact Environmental Services (contact information on this page) to learn more.
Below is a list of locations for City treatments. Bold indicates spray treatments in the last two weeks.
Last update: July 19, 2022
|Areas managed||Treatment Date|
|Dunthorpe/Taylors Ferry/Sam Jackson||4/23/2022|
|Fairfax, etc./Council Crest||4/24/2022|
|Hamilton/Greenhills, etc./Montgomery (pull)||4/27/2022|
|Boones/Taylors Hill/Oaks Bluff/W Fairmount||5/11/2022|
|SE Flavel & Clatsop/SW Cap Hwy/Lesser/Pasadena||5/13/2022|
|Boones Cliff/Tryon Confl/Barbur/Vincent||5/23/2022|
|Skyline (above 26)/Kehoe/Highland||5/24/2022|
|Woods Parks (pull)||5/27/2022|
|NE Fremont/Rocky Butte/Kehoe||6/2/2022|
|SW Shattuck/Skyline (pull)||6/3/2022|
|Inverness/Rocky Butte (pull)||6/14/2022|
Current Phase – Seeds Ripening. Mature seeds ripen for four to six weeks until the plants begin to dry out, typically in early to mid-July. Pulling can be done in this phase, without regard for root re-growth but must stop when plants begin drying. Herbicide treatment will have no effect during this phase and should not be attempted.
Prevention is Best Practice
Clean your boots, pets, and maybe even your tires when you finish a hike or trail ride in Pacific Northwest natural areas, or if you have invasive plants on your own property. Cleaning boots and pets keeps invasive plants from spreading to new places. Be careful when trading plants with neighbors and fellow gardeners to make sure you’re not trading this or any other plant of concern.
Be Aware of Look-alikes
These plants can look like garlic mustard. Here are some tips to tell the difference.
- Fringecup (Tellima grandiflora). This plant has hairy leaves and stems. Garlic mustard doesn’t.
- Piggy-back plant (Tolmiea menziesii). This plant has also hairy leaves and stems. Garlic mustard doesn’t.
- Ground ivy (Glecoma hederacea). Ground ivy leaves have the same shape as garlic mustard seedlings and rosettes, but ground ivy grows along the ground. Garlic mustard grows straight up.
- Hairy bittercress (Cardamine hirsuta). These mustard “cousins” have deeply-lobed leaves, compared to garlic mustard’s simple round or triangular leaves. Hairy bitter-cress is also usually shorter (6-8 inches high) and flowers February through March.
- Black mustard (Brassica nigra). These mustard “cousins” have longer pods than garlic mustard with obvious bumps where the seeds are.
Properly Dispose of Invasive Plants
To prevent spreading invasive plants:
- Never place plants or seeds in your compost or yard debris.
- Never throw pulled plants on the ground or into the street or sidewalk.
- Put all pulled plants, bulbs, or seeds into a plastic bag and put the bag in the trash.
- Wash all garden tools and gloves.