Click for a foliage detail.

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Box elder
Acer negundo

IDENTIFICATION — Box elder leaves have three lobed leaflets that are somewhat pointed. The stems are smooth green to dark red with a white waxy coating that you can rub off with your fingers. Click to see a foliage detail.

A single or multi-stemmed tree that grows up to 75-ft.-tall, box elder is not good to have in your garden. Winged seeds can sprout almost anywhere and new trees can also sprout from the shallow roots, which make it hard to grow anything nearby. In addition, its weak wood breaks easily in storms.

FAVORITE CONDITIONS — Box elder is not picky. Any place in full sun to part shade with moist, even wet soil is fine. It readily adapts to almost any conditions except deep shade or very dry soil.

CONTROL — Pull seedlings if you spot them when they’re young enough. This is the best method in areas where you can’t dig or spray, such as in ground cover beds.

Spray young sprouts in open, mulched areas with nonselective herbicides, such as Roundup^® Poison Ivy & Tough Brush Killer Plus. Always follow the label directions, but you usually apply these products to actively growing weeds in spring or summer.

Digging is the preferred method in beds where spraying a herbicide would be risky for the other plants. Plus, unlike spraying actively growing weeds, digging lets you get rid of box elder any time you can push the shovel into the soil.

Once box elder gets too big to dig, you’ll need to use a saw to remove it. Then dribble or brush on a systemic stump killer around the edges where the sap is flowing. It’s absorbed into the wood and kills the roots.

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Crown vetch
Coronilla varia

IDENTIFICATION — Crown vetch grows up to 2 ft. tall. It has a dense, sprawling habit with stems that can be 5 to 6 ft. long. Pink flowers are followed by 3-in.-long seed pods. Although it’s still being sold and planted, you do not want this near your garden. It can spread quickly with seeds, root and stem pieces, and it’s tough to get rid of.

FAVORITE CONDITIONS — You’ll find this pest in full sun to part shade in rocky or rich soil. Once used to control erosion along roadways, this weed escaped and is forcing out native plants.

CONTROL — Dig crown vetch out of established gardens or use a selective herbicide in turf areas. It’s a perennial, so for the best control, apply herbicide in fall, before the leaves go dormant, and again in spring as the leaves emerge. Repeated mowing also keeps this weeds from producing seeds.

When you’re tackling crown vetch and other weeds with tough roots, a good weeding tool, such as our Soil Knife, really comes in handy.

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Stinging nettle
Urtica dioica

IDENTIFICATION — If you’ve ever walked along a wooded path, you’ve probably encountered stinging nettle. This perennial weed, with bright- to dark-green leaves, can grow to 3 to 6 ft. high. The square stems are covered with fine hairs, which break and release a sap when you brush against the plant. If the sap gets on your skin, it causes a stinging feeling that lasts for a few minutes or longer, depending on how sensitive you are. From May to October, pale green flowers open along the stem between the leaves.

FAVORITE CONDITIONS — You’ll find stinging nettle in damp, fertile, shady locations. In the wild, it grows well along stream banks and at the edge of wooded areas. But it’ll also tolerate more sunny spots, such as an open field or roadside. In the garden, stinging nettle may pop up on bare soil, too.

CONTROL — Stinging nettle spreads by seed and by rhizomes, which allow it to colonize an area quickly. To control small patches or individual plants, pull them by hand, but be sure to wear gloves and long sleeves so you don’t get “stung.” If you’re dealing with a large colony of plants, try mowing them off and using a garden fork to remove the roots. Herbicides, such as glyphosate or 2,4-D, are also effective and spraying them keeps you from coming in contact with the plant.

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Common buckthorn
Rhamnus cathartica

IDENTIFICATION — Growing quickly to a large shrub or small tree up to 20 ft. tall, common buckthorn has sharp spines at the tips of the twigs that can be dangerous as you walk through brushy areas. If you scratch the bark of this woody weed and it’s yellow underneath, you’ve found common buckthorn. Late in fall you’ll also notice that the foliage stays on this pest long after other leaves have fallen. And look closely at the leaves — there are usually three to five pairs of veins in each one.

FAVORITE CONDITIONS — Common buckthorn prefers places in part shade in moist to dry soil.

HOW IT SPREADS — Birds eat and spread the seeds of the 1/4-in.-diameter messy black fruit in fall.

CONTROL — When the plant is a seedling, pull or dig it out of the ground. If it’s too large for this, spray the plant with a nonselective herbicide, such as Roundup^® Poison Ivy & Tough Brush Killer Plus in spring or late summer. Or cut down the tree and dribble or brush on a systemic stump killer around the edges where the sap is flowing. It’s absorbed into the wood and kills the roots. Be careful, it can kill any plant it gets on.

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Gooseneck loosestrife
Lysimachia clethroides

IDENTIFICATION — It may produce attractive arched white flowers in late spring to summer, but this aggressive 3-ft.-tall plant can take over your garden quickly.

FAVORITE CONDITIONS — Gooseneck loosestrife prefers part shade and moist soil. Dry soil and full sun scorch the foliage and slow down the plant’s growth. It’s cold-hardy in USDA zones 4 to 9 and heat-tolerant in AHS zones 9 to 1.

CONTROL — If you want to grow it, contain the roots in a buried plastic pot. The roots can be hard to pull, so digging any time of year is best. You can also use nonselective herbicides.

A BETTER ALTERNATIVE —Nothing else will have those distinctive arching goose necks, but bluestar will have a similar size and texture. Between 2 to 3 ft. tall with an equal spread, it’ll bloom best in full sun to part shade. The clusters of pale-blue flowers open in late spring. Bluestar (Amsonia tabernaemontana) is cold-hardy in USDA zones 3 to 9 and heat-tolerant in AHS zones 9 to 1.

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Common mullein
Verbascum thapsus

IDENTIFICATION — At first glance, this weed could be a tall, striking ornamental for the back of your border. But its soft gray foliage and tall spikes of yellow flowers can be deceiving. It could take over your garden. Just one common mullein plant is capable of producing about 180,000 seeds, which can remain viable in the soil for 100 years or more.

Common mullein, also known as woolly or flannel mullein, is a biennial. The first year it’s a low rosette of gray feltlike leaves that can be more than a foot long. In its second year of growth, cylindrical spikes of small cup-shaped yellow flowers appear. The flower stalk can be up to 8 ft. tall and often blooms from June until early October. Both the leaves and the stem are covered in soft woolly hairs. Spent flower stalks remain standing through the winter.?

FAVORITE CONDITIONS — Found throughout much of North America, common mullein prefers lean, dry sandy soils. But it will adapt and grow just fine in richer soils, too. And like many plants with gray woolly foliage, common mullein needs plenty of sun to reach its full size. Some of its favorite spots are gravelly areas like ditches, railroad embankments or along driveways. Occasionally you’ll find it growing in vacant lots, fence rows or old garden areas that are rarely cultivated.

CONTROL — You can easily pull common mullein plants out by hand, especially in loose or gravelly soil, because they usually have a single taproot. But if you can’t pull a mature plant, make sure to remove any blooms and seed capsules before they spread. To prevent any unwanted seedlings, dispose of the removed stalks in plastic bags that you send away in the trash.

Herbicides are especially effective on young plants. Apply glyphosate, a nonselective herbicide, to the foliage while the plant is actively growing in spring.

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Chicory
Cichorium intybus

IDENTIFICATION — The line between wildflower and weed can be narrow. With chicory, or blue sailor weed as it’s sometimes called, what one person considers a lovely blue flower, a neighbor might consider a weed. This is one of those perennials that can go either way.

In summer, branched flower stems spring up from the center of a low rosette of leaves that looks very much like a dandelion. These tough stems can reach more than 7 ft. tall, but the average is usually less than 3 ft. The leaves along the tough stems are small and not very noticeable. Underground there’s a fleshy taproot that if broken, will “bleed” a milky white sap. But the daisylike flowers (usually blue, but sometimes pink or white) are what you’ll notice first.

Each morning the flowers open facing the rising sun. They last just one day, so by late afternoon they fade and wither. But rest assured there will be more tomorrow morning.

You can eat tender young chicory leaves in salads or as a cooked green. Roots are cooked and eaten or dried and ground to make a coffee substitute.

FAVORITE CONDITIONS — This European native has naturalized across much of North America. You’ll spot it growing along roadsides or the edge of your garden. It does not like areas that are frequently cultivated or mowed to less than 2 in. tall.

CONTROL — Just like a dandelion, chicory spreads mainly by seeds, so you’ll want to keep it from setting seeds. However, pieces of root will also grow quite easily. Repeatedly mowing the plant short, or cutting it off at the soil line will eventually kill it. The taproot is hard to pull from the ground, even after soaking the area with water first. Broadleaf or non-selective herbicides are also effective at getting rid of chicory.

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Fuller’s teasel
Pastinaca sativa

IDENTIFICATION — Originally introduced from Europe for use as a dried flower, Fuller’s teasel has naturalized in much of North America. The first year, this biennial forms a rosette of oblong leaves that may grow to nearly 12 in. long. During the second year, several flower stalks with spines shoot up nearly 6 ft. The spiny egg-shaped lavender flowers bloom from June to October. After flowering and producing seed, the plant dies.

FAVORITE CONDITIONS — Fuller’s teasel prefers open, sunny sites like roadsides and disturbed areas, although it may grow in your lawn or garden. It’s a particular pest for restored prairies and wildlife areas because each plant is capable of producing more than 2,000 seeds and most of them will germinate. Under favorable growing conditions, it can actually outcompete native prairie plants.

CONTROL — As with all biennial weeds, it’s easier to manage Fuller’s teasel in the rosette stage. Use a dandelion-puller to pull out the long tap root or slice it off, below the soil, with a sharp spade. And as with dandelions, be sure to get as much of the root as possible so it won’t resprout. You can cut off the flower head to prevent it from going to seed. Herbicides that contain triclopyr or glyphosate can also be used, but are most effective when applied while the plants are in the rosette stage before they flower.

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Wild parsnip
Pastinaca sativa

IDENTIFICATION — This invasive biennial is related to the edible parsnips you may grow in your vegetable garden. Like its cultivated cousin, wild parsnip has a long, white-yellow taproot that is edible.

The first year, a rosette of leaves emerges and grows to about 1 ft. tall. Egg-shaped leaflets are in pairs along the stem and are deeply toothed or lobed. During the second year it sends up a thick, grooved flower stalk. Bright yellow flowers in flat clusters, like dill, appear from May to October. Flowering plants may grow as tall as 5 ft.

FAVORITE CONDITIONS — Wild parsnip spreads by seed and grows just about anywhere in North America in fields, ditches, prairies, bike paths, cultivated gardens and even your lawn. Although it prefers full sun and moist to wet soils, it will grow in shade and dry soils, too.

CONTROL — Hand digging wild parsnip is the most effective control method. But the deep taproot can make it difficult. If possible, identify and dig up plants when they’re in the rosette stage and the tap root is short and easier to dig. Cut or mow flower stalks on mature plants to prevent seeds from forming. Then dig up as much of the plant as you can. Herbicides that contain glyphosate, such as RoundUp^®, can be an effective control. Follow label directions. Wear long sleeves, pants and gloves when handling wild parsnip because it exudes a chemical that causes photodermatitis blisters when your skin is exposed to sunlight. These can become very painful and may require medical attention.

Click on the photo to see a larger image.

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Prostrate spurge
Euphorbia supina

IDENTIFICATION — The stems and undersides of the leaves of 2-in.-tall prostrate spurge have a red tint. If you break the somewhat hairy stems, they ooze a milky sap.

FAVORITE CONDITIONS — This mat-forming annual weed is often found from summer to fall in dry, gravelly to sandy soil in full sun. It thrives in full hot sun, even coming up in cracks of concrete, and is a prolific seeder.

CONTROL — Despite having a central tap root, prostrate spurge is easy to pull or hoe.

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Common mallow
Malva neglecta

IDENTIFICATION — Common mallow is a relative of hollyhocks that produces pink, pale blue or white summer flowers. It is sometimes called cheeseweed because the seed pods that follow the blooms are shaped like segmented wheels of cheese. These pods turn brown in summer and split open to release seeds.

FAVORITE CONDITIONS — In full sun to light shade and moist soil, common mallow can sprout in fall or early spring, producing flowers and seeds the following summer.

CONTROL — This weed has a short taproot, which makes it easy to pull or hoe.

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American elder
Sambucus canadensis

IDENTIFICATION — A quick way to identify this tree seedling is to crush a stem or a few leaves and you’ll get a disagreeable odor. Break or cut a mature stem and you’ll discover a spongy white pith in the center. And last but not least, the creamy white flowers in spring and the dark purple fruits that follow are in large, flat-topped clusters.

FAVORITE CONDITIONS — Full sun to part shade in moist, fertile soil is where you’re likely to find American elder. It also tolerates moderately dry conditions.

CONTROL — Pull or dig out saplings or spray with a nonselective herbicide like Roundup^®.

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Musk thistle
Curduus nutans

IDENTIFICATION — All the surfaces of the leaves and stems of musk thistle are covered with sharp prickles. The spiny multi-branched stems reach 2 to 6 ft. tall. From summer to fall, its showy red-purple flowers open, the flower heads drooping as they age.

FAVORITE CONDITIONS — The seeds of this biennial weed sprout in summer, in full sun or shade, in areas not regularly cultivated, such as fence rows, garden perimeters and lawns.

CONTROL — Sharp spines make hand-pulling this weed difficult. So hoe the young plants or spray a broadleaf herbicide before the seeds ripen.

PHOTO: © Jerry Pavia

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Chameleon plant
Houttuynia cordata

IDENTIFICATION — Often sold as an ornamental, the leaves of chameleon plant are green with margins of red, bronze or yellow and have a pungent odor when they’re crushed. The plant reaches 6 to 12 in. tall and spreads by underground rhizomes, rooting stems and seeds.

FAVORITE CONDITIONS — It prefers wet soil in sun or shade; in dry shade situations it spreads much slower.

CONTROL — Start digging and keep digging or spray with a nonselective herbicide. If you want to keep some, plant it in a buried container so the roots can’t run.

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Red clover
Trifolium pratense

IDENTIFICATION — Red clover is cultivated as a hay crop in agricultural areas, but is considered a weed elsewhere. It has fuzzy red-pink flowers and a V-shaped marking on each leaf. It can reach 20 in. tall.

FAVORITE CONDITIONS — You’ll most likely find red clover growing in sunny areas along garden edges and perennial borders, but rarely in tilled areas. It’s quite tolerant of wet soil conditions.

CONTROL — The stems of this weed root at nodes wherever they touch the soil. A broadleaf herbicide is the best control.

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Japanese knotweed
Polygonum cuspidatum

IDENTIFICATION — This extremely invasive weed has simple medium-green leaves and spike-shaped pale-green to white flowers in summer. By the end of summer the plant can reach to 8 ft. tall.

FAVORITE CONDITIONS — Japanese knotweed spreads by rhizomes in full sun and dry soil. Cultivated areas, such as garden beds, and waste areas are where you’ll find this pest.

CONTROL — Use a nonselective herbicide like Roundup^® as the plant is starting to go dormant in early fall.

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Buffalo bur
Solanum rostratum

IDENTIFICATION — Buffalo bur grows up to 2 ft. tall and is armed with long yellow spines on its deeply lobed light green leaves and along sturdy stems. In summer, small clusters of bright-yellow flowers form, followed by spiny seed pods.

FAVORITE CONDITIONS — Any dry, exposed soil in full sun is ideal for buffalo bur. Unfortunately, the weed is even drought-tolerant.

CONTROL — The simplest control for buffalo bur is to hoe out the young seedlings. Because of the sharp spines on the flowers, stems and seed pods, wear gloves to pull older plants.

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Eastern poison oak
Toxicodendron toxicarium

Western poison oak
Toxicodendron diversilobum

IDENTIFICATION — As with their close relative, poison ivy, “Leaves of three, let it be” is good advice. Eastern and Western poison oak both have three-leaflet leaves, with red-tinged new foliage and green-white fruit in late summer. Both species grow as small shrubs or vines up to 20 ft. long.

All parts of poison oak contain an oil called “urushiol.” About 90 percent of humans are allergic to this compound, and it causes severe itching and blistering on skin. The more you’re exposed to poison oak, the more likely you are to become sensitive to it, so don’t assume that you’re immune just because you’ve never reacted before.

FAVORITE CONDITIONS — Eastern poison oak is found mainly in the southeastern quarter of the United States, from Florida into Kansas. Western poison oak is found in California, Oregon and Washington and British Columbia. Both species are common in fence rows, waste land, stream banks and wild areas — and unfortunately, also in gardens.

CONTROL — It’s important to remove or kill the entire plant when you’re dealing with poison oak because it regrows from even small portions of the roots. You can pull seedlings or small plants by hand, but be very careful. Urushiol on gloves or clothing can get on your skin, so you’ll need to wash anything you’re wearing — even shoes. Don’t burn the pulled-up plants because inhaling the smoke can cause throat and lung irritation. It’s not a good idea to put them in the compost pile either, so put the plants in a heavy paper bag and dispose of them with your yard waste.

Using herbicide is often the easiest way to get rid of large, old plants. Systemic herbicides with glyphosate (like Roundup^®) will kill poison oak. But it’s most effective when you apply it in late summer, after fruit have formed but before the leaves turn red. You may need to apply it more than once. Because the herbicide will kill any plant it comes in contact with, be careful not to get it on any nearby ornamental plants.

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White clover
Trifolium repens

IDENTIFICATION — This low, 4- to 12-in.-tall spreading weed has white flowers and roots wherever stem nodes touch the soil, but it also spreads by seed. Some folks plant white clover because it adds nitrogen to the soil, which keeps the grass green during heat and drought.

FAVORITE CONDITIONS — White clover thrives in full sun in areas that are rarely tilled, such as lawns and perennial borders.

CONTROL — Broadleaf herbicides, especially those containing 2,4-D, are the most effective means of control for white clover. If you have white clover growing in your lawn, a fall application of nitrogen feeds the grass while it controls this weed.

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Sulfur cinquefoil
Potentilla recta

IDENTIFICATION — This 2-ft.-tall perennial weed blooms with sulfur-yellow flowers from late spring to late summer. The plant has stout, hairy stems and leaves with five to seven deep lobes. It spreads by seeds and also by root pieces that are left in the soil.

FAVORITE CONDITIONS — Sulfur cinquefoil needs a place in full sun and is usually found in dry, alkaline soil in rarely cultivated areas.

CONTROL — Hand pull or hoe, making sure to remove all parts of the root. Broadleaf herbicides containing 2,4-D are also effective.