Common groundsel

About

A small, speedy weed from Europe that can go from seedling to seed in about six weeks and squeeze several generations into one year. It carries pyrrolizidine alkaloids that slowly damage the liver, so keep it out of pastures, hay and anywhere animals graze.

Also called groundsel, old-man-in-the-spring, chickenweed, grundsel, birdseed

How to identify it

Look for

An upright plant, usually under 18 inches, with fleshy, hollow stems that are often purple near the base. Leaves are deeply lobed with irregular teeth. The small yellow flower heads have no petals and are wrapped in green bracts with black tips; they open into white, fluffy seed heads like a tiny dandelion.

Look-alikes

Its petal-less yellow flower heads set it apart from most yellow daisy-type weeds. Its relatives the ragworts (other Senecio species) carry the same liver toxins, so treat any of them as unsafe for animals.

Where it grows

Gardens, nursery pots, vegetable beds, orchards, lawns, pavement cracks and roadsides, especially where the soil stays cool and moist.

When

Sprouts mostly from early spring to early summer and again into fall, and grows year-round along mild coasts; plants can bloom 4-5 weeks after sprouting and drop seed about a week later.

How it spreads

By seed only; a plant typically makes about 1,100-1,800 wind-carried seeds (far more with no competition), and plants pulled while blooming can still ripen about a third of their seeds.

Most common in

Where it is regulated

Washington lists common groundsel as a Class C noxious weed.

What to do, gentlest first

Protect yourself first. Weed killers are a last step; always read and follow the label.

1. Clear edges and clean up after harvest Prevent

   Pull groundsel from path edges, pots and waste spots near the garden before it seeds, and clear beds soon after harvest. It sets seed so fast that one missed round restocks the bed.

2. Pull or hoe before any flowers open By hand

   The shallow, fibrous roots pull out easily and seedlings die when hoed. Get plants before the first flowers open, because cut or pulled plants that are already blooming can still ripen seed.

   Bag blooming plants instead of leaving them on the soil or adding them to compost; wear gloves.

3. Keep beds mulched Barrier

   Most seeds need light to sprout, and seedlings have little ability to push through a dense layer of organic mulch.

4. Spot-treat or use a pre-emergent Conventional spray

   In landscape beds, glyphosate can be used as a spot treatment; in lawns, 2,4-D products work. A pre-emergent broadleaf herbicide can stop seedlings in beds that are always infested.

   Read and follow the label. Many lawn weed killers also kill vegetables and flowers, and glyphosate harms any plant it touches.

Uses, wildlife and pets

For wildlife

Caterpillars of many butterflies and moths feed on the leaves.

Pets

Toxic to dogs, cats and horses (ASPCA, listed as groundsel, Senecio species): its pyrrolizidine alkaloids cause liver damage, and an animal may seem fine before getting suddenly sick. Cattle and horses are more sensitive than sheep and goats.