What is common groundsel?

Easy common groundsel identification starts with the flowers: small yellow heads that look like buds that never quite bloom. It’s a fast annual weed from Europe that loves loose, moist soil, which makes vegetable gardens, fresh mulch and potted plants its favorite places.

Groundsel is not hard to kill, but it’s sneaky. One plant can go from seedling to ripe seed in about five weeks, and you can get several generations in a single season. Miss a few, and next year you’ll be pulling hundreds.

It also matters if you keep horses or cattle or cut your own hay. Groundsel contains compounds that slowly damage the liver, and animals that eat contaminated hay over weeks or months can get sick. For most homeowners, though, it’s simply a nuisance weed that rewards quick, regular attention.

Common groundsel identification: what to look for

Groundsel grows upright or slightly sprawling, usually under a foot and a half tall, with branched, often purplish stems. It’s soft and a little fleshy, not wiry.

• Leaves: Deeply lobed with coarse teeth, a little like a ragged oak leaf. The lower ones have short stalks; the upper ones wrap around the stem.
• Flower heads: Clusters of small, cylinder-shaped yellow heads at the tips of the stems. There are no outer petals; the yellow just peeks out of the top.
• Bracts: Look closely at the green scales around each head. Many of them have a distinct black tip, a handy clue.
• Seed heads: When mature, each head opens into a small white puff of seeds that blow away on the wind, much like a dandelion.

Seedlings have long, narrow seed leaves followed by toothed, egg-shaped true leaves that become more lobed as the plant grows.

Where it grows in Pennsylvania

Groundsel is a cool-weather weed. In central PA, it shows up thickest in spring and again in fall when nights are cool and the soil stays moist. Hot, dry summer spells knock it back, but it often hangs on in shady, damp spots.

You’ll find it in vegetable gardens, freshly mulched flower beds, greenhouse benches, nursery containers and anywhere soil has been turned over. Because the seed blows in on the wind and hitches rides in potted plants, even a brand-new bed can have it within a season.

Common groundsel look-alikes

From a distance, the white puffballs make people think of dandelions. Up close it’s easy to tell them apart: dandelions grow flat with one big petaled flower per hollow stalk and have milky sap, while groundsel is leafy and branched with lots of small, petal-less heads.

Its cousin cressleaf groundsel, also called butterweed, is taller with showy yellow daisy petals and floods wet fields in spring. Pineappleweed is low and bushy too, but its leaves are fine and feathery and the plant smells like pineapple when you crush it.

How to get rid of common groundsel

Good news: this is one weed where pulling it yourself is usually the best answer. The roots are shallow and it comes out with a gentle tug.

• Hand-pull or hoe: Remove plants as soon as you see them, ideally before any flowers form. Shallow hoeing works on flushes of seedlings in garden rows.
• Bag flowering plants: Seeds can keep ripening after a plant is pulled, so don’t leave flowering plants lying in the bed or toss them in the compost pile.
• Mulch: A coarse organic mulch about three inches deep blocks most seedlings in landscape beds.
• Chemical: In lawns, broadleaf herbicides with combinations of 2,4-D, dicamba and MCPP control young groundsel. In beds, glyphosate can be used as a careful spot treatment, but it will damage any plant it touches. Home-use preemergence products don’t do much for groundsel, so mulch and hand-weeding are the backbone.

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

Keeping it from coming back

The whole game is not letting it seed. Walk your beds every week or two in spring and fall and pull anything new. Because the seeds don’t last long in the soil, a couple of seasons of careful weeding can make a real dent.

Keep beds mulched, avoid leaving soil bare after planting, and check the soil surface of new potted plants before you put them in the ground. A thick lawn rarely has groundsel, so reseed thin or bare spots.

If you have animals, keep it out of pastures and hay fields by mowing or pulling patches along the edges before they flower.

Questions we get about common groundsel

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