How to Kill Lily of the Valley

Low-growing lily of the valley (Convallaria majalis) forms a sweet-smelling seasonal ground cover. Although it has lush foliage and perfumed white blossoms in spring, this plant can sometimes turn invasive in the northeastern U.S. and some other select areas. It grows in U.S. Department of Agriculture plant hardiness zones 3 through 8. You have several options to eradicate lily of the valley, ranging from organic controls to pesticide sprays.

All parts of a lily of the valley plant are toxic. Whatever method you choose to eradicate and remove lily of the valley, discard the plant and keep clippings, cut stems and leaves out of the reach of children and pets.

Lily of the valley spreads through underground rhizomes. Use a garden spade to dig out the plant, then rake the area carefully to collect and remove any buried roots. Monitor the planting area. If you missed any rhizomes, they'll sprout again. Repeat the process as necessary. It typically takes up to three digging sessions to fully kill and remove lily of the valley.

If digging out the plant sounds like too much work, try smothering the planting site. This is the easiest organic option for killing lily of the valley.

Lawn mower or string trimmer

Cardboard or newspapers

Mulch

Mow or trim the lily of the valley plants down to the ground using a lawn mower or a string trimmer. Use the lowest setting on a lawn mower.

Cover the mowed site with one or two layers of cardboard or with a 10-sheet-thick layer of newspapers.

Water the area to thoroughly dampen the cardboard or newspaper.

Cover the cardboard or newspaper with a 3- to 4-inch layer of mulch, such as compost, wood shavings or bark chips.

Wait for three to four months. After this time, the buried lily of the valley plants will be fully smothered and killed and will start to decompose, adding nutrients to the underlying soil.

The smothered area should make a good planting site. The combination of soil, cardboard or newspaper and mulch creates a rich planting bed in which seeds or transplants can be directly planted once the waiting period is over.

Soil solarization works similarly to smothering, but it's a much faster process as it channels the power of the sun's ultraviolet rays. Do it during the hottest weeks of the year for the best results. Trim or cut down the lily of the valley plants, water the area to moisten the soil to a depth of 12 inches, then cover the site with a clear plastic tarp. Weigh down the edges of the tarp with rocks or similar heavy objects. The sun's rays penetrate the tarp and bake the underlying soil to temperatures as high as 125 degrees Fahrenheit. After four to six weeks, the lily of the valley will be dead.

Soil solarization doesn't just kill lily of the valley. It also kills other weeds, destroys weed seeds that may be buried in the soil, and wipes out soil-borne fungi and plant diseases.

Thin, 1 mil plastic tarp offers the fastest, hottest soil solarization effects. However, thin plastic tarp also tears easily in the wind. If your garden is in a windy spot, use a 1.5 or 2 mil tarp.

Glyphosate is a broad-spectrum pesticide that kills all plants and works effectively against lily of the valley. Use this option as a last resort if all other options to control the plant fails.

Use any glyphosate-based weed killer spray that comes in a ready-to-spray bottle or pump. Most garden stores or nurseries sell these products. Mist the pesticide onto all exposed green, growing parts of the lily of the valley, including stems and foliage. Wait two weeks, then reapply on any parts of the plant that are still alive.

Glyphosate works best on lily of the valley when outdoor temperatures are 50 degrees Fahrenheit or above.

Glyphosate pesticides are highly toxic. Always follow the labeled guidelines on handling, application and storage. Wear protective clothing when handling the pesticide, including safety eye goggles and gloves. Avoid spraying the product on a windy day, as the wind can carry the spray onto plants that you want to keep. Keep the product out of the reach of children and pets.