Ground Ivy

The creeping mint already in your lawn - and the one plant a forager has to tell from henbit and purple dead-nettle. It runs on stems that root as they go, its round leaves are long-stalked at every node, and it smells strongly minty crushed.

You never plant this - the job is recognizing it. Round scalloped leaves on long stalks, square stems rooting at every node, blue-violet funnel flowers in twos and threes at the leaf joints, and a strong minty smell when crushed.

Nobody should plant ground ivy, so the useful skill is recognition. Look for a creeping perennial two to six inches tall with square stems that run along the ground and root at every leaf joint. Leaves are opposite, round to kidney-shaped, scalloped around the edge, and carried on long stalks at every node — including the topmost ones. In spring it lifts short shoots of blue-violet, two-lipped funnel flowers about half an inch long, purple-spotted inside, in clusters of two or three in the leaf axils. Crushed, any part smells strongly and slightly mustily of mint.

Against henbit (Lamium amplexicaule): henbit stands upright from a single base and its upper leaves are stalkless and clasp the stem in scalloped whorls. Ground ivy creeps, roots as it goes, and every leaf has a stalk. Against purple dead-nettle (Lamium purpureum): dead-nettle also stands upright, and its upper leaves are stalked but triangular and flushed purple, stacked into a fuzzy steeple. Both Lamium are winter annuals with almost no smell that vanish in summer heat; ground ivy is a perennial that is still there in July, and still there in January. Against common mallow, which also has round scalloped leaves: mallow leaves alternate along a round stem and have no mint smell at all.

One more thing to recognize, because it is sold on purpose: the white-edged form Glechoma hederacea 'Variegata' is a common trailing plant in hanging baskets. It is the same plant, it roots wherever a trail touches soil, and it escapes. Do not tip a spent basket out onto the compost heap or the back of the border.

Where it grows tells you something useful. Ground ivy thrives in moist, rich, shaded ground and in thin, compacted, poorly drained turf — conditions in which lawn grass gives up. A creeping Charlie problem is very often a shade-and-drainage problem wearing a disguise.

Control, not care: pull whole runners from damp soil, smother larger patches, fix the shade and compaction that let it in, and treat in autumn with triclopyr if you go chemical. Borax is not the answer.

There is no care here, only removal — and honesty about how hard it is. Ground ivy regrows from any rooted node, so half a job is no job.

By hand. Work when the soil is damp. Start at the edge of the patch, lift the runners and roll them back like a carpet so the rooted nodes come with them, and bag what you pull. Never leave strands lying on the lawn, never compost them, and do not run a tiller or a string trimmer through a patch — both are efficient ways of planting it everywhere else. Expect to go back over the ground several times through a season.

By smothering. On a bed, cardboard or thick black plastic weighted down for a full growing season kills a patch reliably, which is more than most other methods manage.

By fixing the cause. Ground ivy takes ground that grass has already lost. Thinning shade, relieving compaction, correcting drainage, mowing higher and feeding the lawn so it thickens will all hold it back far better than repeated rescue attempts on the same bare patch.

Chemically. If you go this route, timing and active ingredient are everything: a broadleaf lawn product containing triclopyr, applied in autumn after the first light frosts while the plant is still green, gets carried down into the runners with the sugars the plant is storing. Ordinary lawn weedkillers scorch the top and leave the network alive, and spring applications usually regrow. Follow the label, and keep it away from beds and vegetable ground.

And not with borax. The borax recipe that circulates every spring came out of a single set of trials and was later shown to be inconsistent, to injure turf, and to build up in soil to the point where nothing grows well. Iowa State's own extension withdrew the recommendation. Skip it.

One disposal note: ground ivy is toxic to horses in quantity, and the risk is highest from pulled or mown material offered or blown into a paddock. Bag it as household yard waste, well away from grazing animals.

The three answers people need: how to tell it from henbit and dead-nettle before you eat anything, what to do if someone ate it anyway, and why it keeps coming back.

“Is this ground ivy, henbit or purple dead-nettle?” Three checks, in this order. Does it creep and root along the stem? If yes, ground ivy. Do the top leaves have stalks? Ground ivy: yes, every leaf. Henbit: no, they clasp the stem. Dead-nettle: yes, but they are triangular and purple-flushed. Does a crushed leaf smell minty? Ground ivy does, strongly. The other two barely smell at all.

“I ate some.” A stray leaf in a mixed salad is not an emergency, and there is no need to panic over one. But do not eat it as a green in quantity, do not drink it as a regular tea, and do not use it in pregnancy or if you have liver or kidney trouble — it contains pulegone, the compound that makes pennyroyal a genuine poison. If a child has eaten a real quantity, or if anyone has taken concentrated ground ivy or pennyroyal oil, call poison control immediately and do not wait for symptoms. Throw out a picking with ground ivy in it rather than sorting it at the sink.

“My horse or cow got into it.” Ground ivy is toxic to horses in quantity, most often from mown or pulled material that ends up in a paddock. Call a veterinarian promptly, and never dump clippings where livestock can reach them.

“It came straight back.” Almost always because rooted nodes were left in the ground, fragments were spread by a mower or tiller, or spring treatment burned the top and left the runners. Pull whole runners from damp soil, or treat in autumn.

“Will the borax recipe work?” No — it is inconsistent, it damages turf, and boron accumulates in soil where nothing then grows. The recommendation was withdrawn by the extension service that first published it.

“It is only in the shady half of the yard.” That is the diagnosis, not a coincidence. Ground ivy colonizes damp, shaded, compacted ground where turf has thinned. Fix that and you change the outcome.

Alehoof: the herb English brewers used to clarify and flavour ale before hops, carried to North America on purpose as a medicine and a brewing plant - and then never got rid of.

Ground ivy's old names are a record of what it was for. Alehoof and gill-over-the-ground both point at beer: before hops became standard in English brewing, ground ivy was one of the bitter herbs used to clarify and flavour ale and help it keep, and ‘gill’ traces to the Old French guiller, to ferment. Herbalists from Gerard to Culpeper listed it for coughs and inflamed eyes, and it kept a place in country medicine long after hops had taken its brewing job away.

That usefulness is exactly how it crossed the Atlantic. European settlers brought it deliberately, as a medicinal and brewing herb that would grow in shade with no attention — and it has been repaying that favour ever since. It is now naturalized through most of the United States and southern Canada and is one of the most complained-about lawn weeds in the country.

The honest modern footnote is that a long tradition of use is not a safety finding. Ground ivy's essential oil is rich in pulegone, the same compound that makes pennyroyal hepatotoxic, and the historical dose — a bitter note in a barrel of ale — has very little to do with brewing a mug of it every morning. Its real value today is as a plant to know on sight: in the lawn, and in the basket.

Hardy roughly zones 3-10 and at its worst in the humid East, Midwest and Pacific Northwest, wherever ground is shaded and damp; least troublesome in the hot, dry Southwest.

Ground ivy is naturalized across nearly all of temperate North America, roughly zones 3-10, and what limits it is not cold but dryness and sun. It is at its most aggressive where summers are humid and ground stays moist — the Northeast, the Midwest, the Ohio and Mississippi valleys, the Southeast, and the Pacific Northwest — and especially under trees, along north-facing house walls, and in any lawn that is shaded, compacted or poorly drained.

In the arid Southwest and on hot, dry, sunny sites it is far less of a problem: unirrigated ground in full sun stops it. In the coldest zones the top can burn back in an open winter, but the runners survive and the mat closes again in spring; in mild-winter regions it simply stays green year-round, which is a useful identification clue in January when henbit and purple dead-nettle are still seedlings.

Practically, that means the same patch of yard behaves differently across the country, but the diagnosis travels: if ground ivy is winning, the ground is shadier, damper or more compacted than the grass can cope with.