Warm-Season Weeds

Learn about weeds that thrive when summer heat arrives.

By: Julie Martens Forney

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Photo By: Image courtesy of Preen

Photo By: Photo by Julie Martens Forney

Photo By: Image courtesy of Preen

Bull Thistle (Cirsium vulgare)

This spiny weed is a familiar face along roadsides, and if it pops up in your yard, you’ll be dealing with a prickly problem. Spines cover leaves and stems, which are topped with eye-catching lavender blooms. Grab your leather gloves and deal with this weed as soon as you spot it.

Bittersweet Nightshade (Solanum dulcamara)

A cousin of tomatoes, bittersweet nightshade sports purple flowers that fade to form red berry-like fruits. This perennial weed thrives in moist soil and shady spots. In cold regions, plants die to the ground with frost and resprout from roots in spring. In warmer zones, plants linger year-round, forming thick woody stems.

Wild Carrot (Daucus carota)

Known most often by the name Queen Anne’s lace, wild carrot forms a deep taproot and is actually a wild ancestor of carrots grown in garden today. Lacy blossoms appear on two-year-old plants. Use care allowing queen anne’s lace to grow in your yard. If plants set seed, you could be in for an invasion.

Purslane (Portulaca oleracea)

Succulent, fleshy leaves and stems indicate that this weed can thrive with little water. It tends to grow in cracks and crevices—anywhere it can gain a root hold. Take care to dig carefully to remove all root pieces when pulling, because any roots left behind can sprout new plants. Purslane also spreads by stems that root where they touch soil and by seeds that follow yellow flowers.

Burdock (Arctium minus)

Burdock produces purple flowers fade to form prickly seedheads that hook onto clothes and pet fur. Leaves are large and green on top and felty white beneath. Burdock is a biennial. That means it produces a tuft of leaves the first year of growth, followed by a flowering stem the second year. Deal with it as soon as you spot it.

Foxtail Grass (Setaria viridis)

Foxtail grass earns its name from the bristly seedhead that’s up to 6 inches long. Plants form grassy clumps that are sometimes upright, sometimes spreading. This is an annual grass that grows from seeds dropped at the end of the previous growing season. Hand pull or mow to keep seeds from forming.

Redroot Pigweed (Amaranthus retroflexus)

A summer annual weed, redroot pigweed brings red stems and roots to the scene. The root is a taproot that’s easiest to pull when soil is wet and plants are young. Plants form stiff, prickly seed clusters at stem ends. Left alone, plants can soar to as much as 8 feet.

Velvetleaf (Abutilon theophrasti)

The weed in this photo is the short broadleaf plant tucked between the narrow blades of a Siberian iris. Leaves are, as the name suggest, velvety to the touch. Flowers are easy to overlook, forming at the base of leaves. Stems are jointed and tall, reaching up to 5 feet. This weed is also called Indian mallow and buttonweed. Pull plants as soon as you see them.

Ladysthumb (Polygonum persicaria)

Also known as smartweed, ladysthumb grows with jointed, branched stems that form a low, spreading mound. Knobby flowers resemble clusters of individual balls and form at stem ends. Blooms offer shades of pink and white. This plant spreads readily to form colonies and resprouts from root pieces left in soil. Dig carefully when hand pulling.

Lambs Quarters (Chenopodium album)

This common weed appears in most yards at some point. Leaves have a triangular to oval shape and a white coating that rubs off when you touch it. Flowers form in soft spikes at stem ends. Pull young plants and use in salads as a spinach substitute. Mature plants can grow to 5 feet tall.

Yellow Woodsorrel (Oxalis stricta)

This weed resembles a three-leaf clover topped with cheery yellow flowers. Plants are technically a perennial, but perform like a warm-season annual. Look for woodsorrel in gravel areas, mulched beds, vegetable gardens—any location can host this weed. Seed pods explode to spread seeds over a wide area. Try to pull plants before seed pods form.

Crabgrass (Digitaria sanguinalis)

If you tend a lawn, you’ve probably encountered crabgrass. This annual grass tends to grow in ground-hugging clumps, but sometimes forms upright stems. Treat for crabgrass in lawns early in the growing season, using a pre-emergent weed killer that interrupts crabgrass seed germination.

Prostrate Spurge (Euphorbia sp.)

A low, spreading weed, prostrate spurge tends to pop up in driveway cracks, brick patios and gravel beds. Pink stems hug the ground and have milky, sticky sap. Wear gloves when pulling this weed to avoid sticky, dirt-covered fingers. Small green flowers and seeds form along stems at leaf bases. If you plan to hand-pull this weed, wait until plants are large enough to grab and soil is moist.

Nutsedge (Cyperus esculentus)

A perennial weed, nutsedge falls into the weedy nightmare category. Roots form nutlets underground roughly the size of popcorn kernels. Try to pull plants, and you’ll often leave nutlets behind, which each produces a new plant. Plants also produce bur-like seedheads. Nutsedge tends to grow where soil drains poorly. You’ll need weedkillers to get rid of this weed.