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Wild Mustard

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Pennsylvania weed ID · Garden & field annual

Wild Mustard

Sinapis arvensis · Brassicaceae (mustard family)

Summer annual (some fall-emerging plants overwinter)
Broadleaf
Non-native

Bright yellow flowers popping up all over a freshly graded yard or a new garden plot are often wild mustard. It's easy to control, as long as you get it before the pods ripen.

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Quick ID

Bright yellow four-petaled flowers on a branching plant
Rough, hairy, wrinkled leaves, lower ones lobed
Skinny upright pods with a distinct flattened beak
Flowers and pods on the plant at the same time
Shows up on freshly disturbed soil

Fact sheet

Scientific name: Sinapis arvensis
Family: Brassicaceae (mustard family)
Also called: Charlock, Field mustard, Brassica kaber
Life cycle: Summer annual (some fall-emerging plants overwinter)
Native to PA?: No — native to Europe, Asia and North Africa
Height: About 1–3 ft, branching
Leaves: Alternate; lower leaves large, coarsely toothed and often deeply lobed, on stalks; upper leaves smaller, lance-shaped and stalkless or nearly so; stiff scattered hairs give a rough, wrinkled feel
Flowers: Bright yellow, four-petaled, about 1/2 in across, in clusters at the branch tips; late spring through summer
Seeds / fruit: Upright, slender, hairless pods 1–1.75 in long ending in a flattened, angled beak; small round reddish-brown to black seeds
Roots: Taproot
Spreads by: Seed only — seeds can stay alive in the soil for many years, especially when buried
Where you’ll find it: Crop fields, gardens, new seedings, disturbed soil, roadsides and construction sites
When you’ll see it: Mostly emerges in spring once soil warms past about 40°F, with a smaller flush in fall; flowers and pods often present together through summer
Toxicity: Seeds contain compounds that can harm livestock eating large amounts of mature plants or seed; not a concern for handling
PA status: Not regulated in PA
Difficulty to control: Easy
Best time to act: Pull, hoe or spray young plants in spring before flowering; never let pods ripen

What is wild mustard?

Wild mustard identification is mostly about two things: four-petaled yellow flowers and slender pods ending in a flattened beak. It’s an annual in the mustard family that came from Europe and Asia. It’s a classic farm weed, and it shows up in home yards whenever soil gets turned over.

Wild mustard grows fast. In northern areas, plants can flower within three to six weeks after emerging and set seed several weeks after that.

Its real staying power is in the seed. Most seeds near the surface die off within a few years, but some buried seeds can survive for decades and sprout when digging or grading brings them up.

Wild mustard identification: key features

Flowers: bright yellow, four petals in a cross shape, about half an inch across, clustered at the tips of the branches.
Leaves: lower leaves are large, coarsely toothed and often deeply lobed on stalks. Upper leaves are smaller, lance-shaped and sit close to the stem. Stiff, scattered hairs make the leaves feel rough and look wrinkled.
Stems: branching, with stiff hairs that are thickest near the base.
Pods: upright, slender and hairless, roughly 1 to 1.75 inches long, ending in a flattened, angled beak. Flowers at the top and pods below are often on the plant at the same time.
Seedlings: kidney- to heart-shaped seed leaves, followed by true leaves with wavy, irregular teeth.

Plants usually reach 1 to 3 feet tall.

Where it grows in Pennsylvania

Wild mustard is found across the state in crop fields, gardens, roadsides and any ground that’s been disturbed. It’s most common where soil has been tilled, graded or dug, like new home sites, freshly seeded lawns, utility trenches and garden expansions.

It responds strongly to rich, fertilized soil. In central PA, it often shows up the first spring after an excavation or regrading project, when buried seed from old farm ground is brought to the surface.

You may also notice it along the edges of farm fields and hay ground that border residential lots, where seed blows or washes into yards and gardens.

Wild mustard look-alikes

Several yellow-flowered mustards bloom in Pennsylvania. Yellow rocket is the most common mix-up. It blooms earlier, in April and May, and has smooth, glossy, dark green leaves with a large, rounded end lobe. Wild mustard’s leaves are rough and hairy.

Wild radish has veined petals in yellow, white or purple and beaded pods. Field pennycress has small white flowers and flat, round pods. Wild parsnip has yellow flowers in flat umbrella-shaped clusters. It’s a different plant entirely, and its sap can burn your skin in sunlight, so get the ID right before you pull.

How to get rid of wild mustard

Wild mustard is one of the easier weeds to manage. It’s an annual that spreads only by seed, so stopping seed is the whole game.

Pull or hoe: young plants pull easily, taproot and all, especially in moist soil. Hoe seedlings in the garden on a dry day.
Mow before seed: on a big, freshly graded area, mowing before the pods mature prevents a new seed crop. Mow again if plants re-flower lower down.
Get grass established: on new lawns, a quick, thick stand of grass shades out mustard. Mowing a new seeding usually takes care of it as the turf fills in.
Mulch beds: 2 to 3 inches of mulch stops most seedlings in landscape beds.
Herbicides: mustards are generally sensitive to lawn broadleaf herbicides containing 2,4-D, often combined with dicamba and MCPP. Treat young plants in spring before flowering. Check the label before using any product on a new seeding, since many require the grass to be mowed several times first.

Read and follow the herbicide label (the label is the law) and confirm it’s labeled for your site, whether lawn, beds or a vegetable garden. Applying herbicides for hire in Pennsylvania requires a PA Department of Agriculture pesticide applicator certification, so large areas should go to a licensed lawn-care company.

Keeping it from coming back

Don’t let it go to seed, even once. A single season of pods can restock the soil for years. Pull or mow plants as soon as the yellow flowers appear.

Limit soil disturbance once an area is established. Every time you till or dig, you bring buried seeds to the surface. Seed or mulch bare soil quickly after any project, and keep lawns thick so new seedlings don’t get light. A few years of preventing seed will steadily shrink the problem.

Watch the first spring after any excavation, grading or drainage work. That’s when buried seed is most likely to wake up, and pulling a few early plants is far easier than battling a yard full of pods in July.

Questions we get about wild mustard

Why did wild mustard show up after my yard was graded?

Its seeds can survive buried in soil for a long time. Grading or digging brings them up to the surface, where they sprout.

Is wild mustard poisonous?

It's not a handling hazard. Large amounts of mature plants or seed can harm livestock, so keep it out of pastures and hay.

How do I tell wild mustard from yellow rocket?

Yellow rocket blooms earlier and has smooth, glossy leaves. Wild mustard has rough, hairy leaves and pods ending in a flattened beak.

Will mowing kill it?

Mowing before pods mature stops seeding, and in a lawn, repeated mowing and thick grass usually eliminate it.

Weeds taking over a bed, slope or wet spot?

After excavation or grading work, our crew seeds or sods disturbed soil promptly so weeds like wild mustard don't get a head start. We rebuild beds, regrade and drain wet ground, clear overgrown brush and build patios and walls across Clinton, Lycoming, Centre and Union counties.

Get a free estimate (570) 397-9800

Similar weeds

Yellow RocketBarbarea vulgaris

Field PennycressThlaspi arvense

Shepherd's PurseCapsella bursa-pastoris

Photos: Wikimedia Commons contributors, credited under each photo (used under their Creative Commons or public-domain licenses).
Further reading: Penn State Extension
Herbicides: always read and follow the product label. Applying pesticides for hire in Pennsylvania requires PA Dept. of Agriculture certification.

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