Poison hemlock

About

A tall European weed in the carrot family that is deadly if eaten, by people, pets or livestock. It is spreading along roads, ditches, creeks and field edges, and it looks a lot like wild carrot and parsley.

Also called deadly hemlock, spotted hemlock, poison parsley, spotted parsley

How to identify it

Look for

Smooth, hairless, hollow stems are marked with purple or red spots and blotches. Leaves are glossy, finely cut and fern-like, and crushed leaves smell musty, like mouse urine. In its second year it grows 3 to 8 feet tall with many small, umbrella-shaped clusters of white flowers; the first year it is a low leafy rosette.

Look-alikes

Wild carrot (Queen Anne's lace) rarely tops 2 feet and has densely hairy stems without purple spots; poison hemlock is taller and smooth-stemmed. Water hemlock, which is even more deadly, and giant hogweed can also be confused with it, so never eat any wild carrot-family plant.

Where it grows

Roadsides, ditches, creek banks, field edges, pastures, fence lines and neglected garden corners, especially in moist soil.

When

Forms a leafy rosette the first year, then bolts and flowers in late spring and summer (about June to August) the second year before setting seed and dying.

How it spreads

Spreads only by seed, which can stay alive in the soil for several years.

Most common in

What to do, gentlest first

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

1. Learn it and suit up Prevent

   Learn the purple-spotted, hairless stem. Wear gloves, long sleeves and eye protection whenever you handle it, and keep kids and pets away.

   Keep livestock out of infested spots and never feed hay that has hemlock in it.

2. Dig first-year rosettes By hand

   Dig out small plants with their long taproot while they are still low rosettes, before they flower and seed.

   Wear gloves. Bag plants for the trash, never burn them or leave them where animals can reach, and don't compost seed heads.

3. Pelargonic acid burndown on small rosettes Organic spray

   A pelargonic acid (fatty-acid) product can burn down small, first-year rosettes. Expect to repeat it, since roots may resprout.

   It kills any plant it touches. Wear gloves and read the label.

4. Treat rosettes with 2,4-D or glyphosate Conventional spray

   Spray first-year rosettes and young plants in spring or early summer, not tall flowering plants. Repeat for several years to use up the seed bank.

   Read and follow the label. Many lawn and brush herbicides also kill garden plants, so keep spray and drift off anything you want to keep.

Uses, wildlife and pets

Pets

Toxic to dogs, cats and horses (ASPCA); signs include drooling, tremors, diarrhea and paralysis, and it can kill.