Prickly Lettuce
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Pennsylvania weed ID · Garden & field annual
Prickly Lettuce
Lactuca serriola · Asteraceae (aster family)
- Winter annual
- Broadleaf
- Non-native
That tall, milky-sapped weed that shot up along your driveway or out of the gravel by the patio, with a row of prickles under every leaf, is almost certainly prickly lettuce.
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What is prickly lettuce?
Prickly lettuce is a weedy wild relative of garden lettuce that came from the Mediterranean and now grows across North America. It loves dry, disturbed ground, so it turns up on construction sites, roadsides and the edges of driveways and patios. Prickly lettuce identification is easy once you know two tricks: look for prickles under the midrib, and break a leaf to see the milky sap.
It usually sprouts in fall or early spring as a low rosette, then shoots up a tall stem in summer, flowers and dies. Because each plant releases fluffy wind-blown seed, one plant in a gravel bed can seed the whole neighborhood.
Prickly lettuce identification: what to look for
The plant looks quite different as a rosette and as a tall summer weed, but the leaves give it away at any stage.
- Leaves: Blue-green, toothed or deeply lobed, with a pale midrib. Flip one over and you’ll find a single row of stiff prickles running down the underside of that midrib. Leaf edges are also lined with small prickles.
- Clasping base: On the stem, each leaf wraps partway around it with two pointed, ear-like lobes.
- Vertical leaves: In full sun, the stem leaves twist to stand on edge, often lining up roughly north and south. That’s why it’s sometimes called compass plant.
- Sap: Every part bleeds white milky sap when broken.
- Flowers and seed: In mid to late summer, an open, branching top holds many small, pale yellow flower heads. These turn into tufts of white fluff, each carrying a single seed.
Where it grows in Pennsylvania
Prickly lettuce prefers sunny, well-drained, disturbed ground. Typical spots are new construction, freshly graded yards, gravel driveways and parking areas, roadsides, field edges, neglected beds and the edges of patios and walks. Its long taproot lets it handle dry spells that wilt shallow-rooted weeds.
It rarely survives in thick, mowed lawn. If you’re finding it in turf, the grass is thin or the area was recently disturbed.
Hardscaped yards see a lot of it. The hot, dry strip where a patio meets the lawn, the gravel behind a retaining wall and the joints of an older walkway are exactly the kind of sunny, open ground this weed likes.
Prickly lettuce look-alikes
The most common mix-up is spiny sowthistle. Both have milky sap, yellow flowers and prickly leaves, but sowthistle has no prickles down the midrib, its leaves stay flat instead of turning on edge, and the leaf base hugs the stem with rounded lobes. Sowthistle flower heads are also larger.
Young rosettes can resemble dandelions, but dandelions never grow a tall, leafy stem and their leaves aren’t prickly. Thistles are spiny all over and have purple flowers.
How to get rid of prickly lettuce
Since it’s an annual that spreads only by seed, the job is simple: get it out before it flowers. Most homeowners can handle this without chemicals.
- Pull or dig: Rosettes and young plants pull easily from moist soil. For older plants, use a weeding fork to get the taproot. Wear gloves if the milky sap bothers your skin.
- Cut before seed: If you can’t pull it, cut the plant off at ground level before it flowers in July. Plants cut too high may branch and flower again.
- Mulch beds: Keep 2 to 3 inches of mulch in landscape beds so wind-blown seed can’t reach bare soil.
- Paver and gravel edges: Seeds love to lodge in open joints and gravel. Keep paver joints filled and topped up, and pull seedlings while they’re small. Joints filled with polymeric sand hold up far better than loose sand, which washes out and leaves a perfect seedbed.
- Herbicide: In lawns, broadleaf products containing 2,4-D, dicamba or MCPP work on rosettes in fall or early spring. Larger flowering plants are much harder to kill, so treat early.
Read and follow the product label; the label is the law. Make sure the product is labeled for the site, since a lawn product isn’t necessarily labeled for beds, gravel or around ornamentals. Anyone applying herbicide for hire in Pennsylvania needs a PA Department of Agriculture pesticide applicator certification, so for big areas hire a licensed lawn-care company.
Keeping prickly lettuce from coming back
The good news is that prickly lettuce seed doesn’t last long in the soil compared to many weeds. A couple of seasons of pulling plants before they seed makes a big difference.
The catch is that seed blows in from roadsides and empty lots. Keep beds mulched, seed or plant disturbed areas promptly, and keep gravel and paver joints tight. Pulling a few seedlings each spring is far easier than dealing with six-foot plants in August.
Questions we get about prickly lettuce
Is prickly lettuce edible?
It's a relative of garden lettuce and young leaves are sometimes eaten, but they're bitter and prickly. The milky sap can also irritate sensitive skin. It's not worth it.
Why do the leaves of prickly lettuce point straight up?
In full sun, the leaves twist on edge, often lining up north to south. It's thought to help the plant handle heat and drought. That's why it's called compass plant.
How do I tell prickly lettuce from sowthistle?
Flip a leaf over. Prickly lettuce has a row of prickles down the underside of the midrib; sowthistle doesn't.
Why is prickly lettuce growing in my patio joints?
Its fluffy seed blows in and lodges in gaps in pavers and gravel. Keeping joints full of polymeric sand and pulling seedlings early stops it.
Weeds taking over a bed, slope or wet spot?
If weeds like prickly lettuce keep sprouting between your pavers, re-sanding the joints with polymeric sand as part of a hardscape tune-up closes the gaps they're rooting in. 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) 397-9800Similar weeds
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.