What is yellow rocket?

Simple yellow rocket identification starts with the timing: it’s the bright yellow mustard that floods fields and roadsides in mid-spring. Also called wintercress, it’s a biennial in the mustard family from Europe and Asia. In its first season it forms a low rosette that stays green all winter, and in its second spring it sends up flowering stalks, sets seed and dies.

Yellow rocket is mostly a problem in hay fields, pastures, new seedings and gardens. It doesn’t handle regular mowing well, so in a lawn it usually means the turf is thin or newly seeded.

The good news is that it’s one of the easier weeds on this list. It doesn’t spread by roots, it doesn’t come back from pieces, and it dies on its own after it seeds.

Yellow rocket identification: what to look for

Yellow rocket is easy to spot in bloom and not much harder in the rosette stage.

• Rosette leaves: Glossy, dark green and smooth. Each leaf has a large, rounded end lobe and one to five pairs of small side lobes along the stalk.
• Stem leaves: Smaller, toothed or shallowly lobed, and clasping the stem.
• Flowers: Bright yellow, about a third of an inch across, with four petals in a cross shape. They’re packed in clusters at the stem tips.
• Seed pods: Slender, upright, four-sided pods about an inch long with a short beak, held close to the stem.
• Stems: Smooth and ridged, branching near the top, usually one to two feet tall.

The whole plant is generally hairless, which helps separate it from several other mustards.

Where it grows in Pennsylvania

Yellow rocket is common across Pennsylvania. In central PA, you’ll see it filling hay fields and pastures in river valleys, along roadsides and field edges, in new grass seedings, and in garden beds that were left bare over winter. It prefers moist, fertile soil but grows almost anywhere it gets sun.

Because it germinates in late summer and fall, ground that’s tilled or seeded then and left thin is likely to have rosettes by the next spring. In hay, it’s more than cosmetic. Heavy stands lower forage quality, and animals generally avoid it.

Yellow rocket look-alikes

Several yellow-flowered mustards bloom in Pennsylvania. Wild mustard is the closest match, but its leaves and stems are rough and hairy, and it’s an annual that usually blooms a bit later. Field pennycress has white flowers and round, flat pods.

Garlic mustard grows in shady spots in spring too, but its flowers are white and its leaves smell like garlic. Cressleaf groundsel, also called butterweed, turns wet fields yellow at the same time, but its flowers are daisy-like with many petals.

How to get rid of yellow rocket

As a biennial that spreads only by seed, yellow rocket isn’t hard to manage if you stop it from seeding. For a few plants, pulling them yourself is often the best answer.

• Hand-pull or dig: Remove rosettes or young plants with a weeding tool, getting most of the taproot. Damp soil makes it easier. Pull flowering plants before pods form.
• Mowing: Regular mowing keeps it from flowering in lawns and along field edges. In hay fields, timing the first cutting before seed pods ripen helps.
• Cultural: A thick lawn or vigorous pasture leaves little room for rosettes to establish. Overseed thin areas in late summer and avoid leaving soil bare over winter.
• Chemical: In lawns, broadleaf herbicides containing 2,4-D, dicamba, MCPP or fluroxypyr, or combinations, control yellow rocket best at the rosette stage in fall or early spring. Once it’s flowering, control drops off, and mowing or pulling is the better choice.

Always read and follow the product label (the label is the law), and make sure the product is labeled for your site, whether lawn, garden or pasture. Applying herbicide for hire in Pennsylvania requires a PA Department of Agriculture pesticide applicator certification, so larger jobs go to a licensed lawn-care or vegetation-management company.

Keeping it from coming back

The most important step is to keep it from setting seed. Each plant can produce a lot of seed, and that’s where next year’s crop comes from. Walk your property in fall and early spring to find rosettes while they’re small, and deal with them before the stalks shoot up.

In gardens, mulch or plant a cover crop instead of leaving soil bare over winter. In lawns, mow at three to three and a half inches and fertilize in the fall to keep the grass dense. Be careful with hay or straw from fields where it’s thick, since it can carry seed.

If you’re seeding a new lawn, expect some yellow rocket the first spring. Regular mowing usually takes care of it as the grass thickens, so there’s rarely a need to panic over a few plants in new turf.

Questions we get about yellow rocket

Similar weeds

Wild MustardSinapis arvensisGarlic MustardAlliaria petiolataField PennycressThlaspi arvense