No Title 1040
As a child, you delighted in the bright yellow flowers of the dandelion. You may have even picked a bouquet of dandelions for your mom, and you probably blew on the feather-like top of the plant, unknowingly propelling seeds through the air. You didn’t realize that the roots could be cleaned, dried, and roasted to make a delicious coffee. You just thought the abundant yellow flowers were pretty.
Today, those yellow flowers probably arouse different actions, sending you running to the store for weed killer or reaching for a garden tool to extract the long, stubborn root. After all, you now know that dandelions are weeds.
It’s that time of year again—time for the annual war of the weeds to begin in earnest. We have enlisted help from two experts: Pat Haragan, a botanist by training, the author of two books, and a former curator of the University of Kentucky College of Agriculture Herbarium; and Dr. J.D. Green, a weed science specialist with the University of Kentucky Cooperative Extension Service. They have identified 15 of the weeds you are most likely to see in your lawn and garden. Green has also provided some advice on controlling weeds.
But what exactly is a weed and how does it differ from other plants?
Poet Ralph Emerson defines a weed as “a plant whose virtues have not yet been discovered.” Weed lovers such as Haragan find that definition the most pleasing; she adds, “Weeds are aesthetically beautiful.”
Haragan follows the movement of weeds throughout the country; she enjoys studying weeds because many are cosmopolitan and come from all over the world, and because they have a “sense of adventure,” popping up in unlikely places such as cracks in sidewalks.
“Perhaps a weed is a plant that people want out of the way,” concludes Dr. John Thieret, professor emeritus at Northern Kentucky University and one of the foremost taxonomic botanists in the country. Thieret points out that there is “a world of difference between a huge patch of morning glory in a soybean field (hindering harvest) and a little specimen of Mollugo verticillata (carpetweed) at a roadside hindering nobody.”
Whether they consider weeds friend or foe, Haragan, Thieret, and others say that what most of us think of as weeds have certain characteristics. Weeds are opportunistic: they thrive in disturbed sites, have been associated with humans throughout civilization, and reproduce rapidly, often by several means (seeds, taproots, and runners) rather than just one. They also have enormous seed production. Each plant of the common purslane, for example, can produce 200,000 seeds each year.
The information on 15 common weeds in Kentucky comes from Haragan and her book Weeds of Kentucky and Adjacent States: A Field Guide. Learning to identify them is the first step to controlling them, whether you wish to eliminate them from your property, cultivate them for flower arrangements, or just brew a cup of dandelion coffee.
15 COMMON WEEDS
Photos courtesy of Pat Haragan
Note: Although some of these weeds/herbs are known for their medicinal or edible qualities, as noted below, we in no way advocate their use in such a manner.
Perennial: a plant that lives for three or more years.
Summer annual: a plant that starts from seed in the spring and dies in the same year.
Winter annual: a plant that starts from seed in autumn, develops a rosette of basal leaves before winter, then flowers and sets seed the following spring or summer.
Ground ivy (Glechoma hederacea)
Life cycle: perennial herb
Earmarks: plant creeps along the ground; rounded leaves; purplish-pink to blue tube-like flowers.
Also called alehoof or gill-over-the-ground, this aromatic herb was the most widely used seasoning in brewing ale until the German discovery of hops. It contains a bitter, volatile oil that is poisonous to cattle that eat the green or dried leaves mixed in hay or fodder.
Common chickweed (Stellaria media)
Life cycle: winter annual
Earmarks: delicate white flowers with deeply notched petals, usually in small clusters at the tips of the stems.
Rich in copper, phosphorous, and iron, this weed is eaten as a salad green or vegetable in many countries. It is also relished for food by wild birds as well as domestic fowl.
Prostrate knotweed (Polygonum aviculare)
Life cycle: summer annual
Earmarks: a sprawling plant with jointed stems and tiny whitish-pink flowers.
The tiny seeds of this plant may be ground into a flour that is similar to buckwheat and can be used in baking cookies, pancakes, and breads. In folk medicine, the fresh or dried stems are gathered during the flowering season, and used in the belief that they cure diarrhea in farm animals. Prostrate knotweed thrives in compacted soil.
Prostrate spurge (Euphorbia maculata)
Life cycle: summer annual
Earmarks: stems often mat-forming; leaves usually marked with a reddish-purplish blotch in the center; tiny, greenish flowers.
These plants contain toxins that cause severe irritation and lesions in the mouth, stomach, and intestines of both humans and livestock.
Common purslane (Portulaca oleracea)
Life cycle: summer annual
Earmarks: freely branched stems that often form mats and small, yellow flowers. Leaves and stems are succulent (hold water).
Used by Native Americans, this weed is valued for its supposed power to ward off magic spells cast upon people or their cattle. It was spread around beds as protection from evil spirits that would visit the sleepers at night. In Europe, the plant has been grown as a garden vegetable. Its fleshy leaves and young stems are still used as salad greens and cooked vegetables.
Hairy bittercress (Cardamine hirsuta)
Life cycle: winter annual
Earmarks: leaves mostly at the base of the plant; white, tiny flowers; seed pods are slender and ascending.
Bermuda grass (Cynodon dactylon)
Life cycle: perennial herb
Earmarks: grass is wiry, often mat-forming, with 3-7 fingerlike clusters that radiate from the end of the stem.
Often planted in lawns, golf courses, and pastures, Bermuda grass is considered one of the worst hay fever-causing grasses in the U.S. It spreads astonishingly fast because each of its numerous joints takes root. In Mexico, the entire plant is made into a concoction thought to heal complaints of the liver, spleen, and kidneys.
Violet (Viola papilionacea)
Life cycle: perennial herb
Earmarks: heart-shaped leaves produced on long stalks; flowers are showy, bluish-purple, and spurred in the back.
The lovely violet is considered a troublesome lawn weed throughout Kentucky, in fact one of the most troublesome. Violets were some of the first flowering plants to be grown commercially and were sold in the markets in Athens around 400 B.C.
Dandelion (Taraxacum officinale)
Life cycle: perennial herb
Earmarks: has a thick taproot with leaves at the base of the plant; bright yellow flower heads on a tube-like stem.
The name dandelion comes from the French word dent de lion, meaning lion’s tooth, and refers to the deeply cut leaves with their tooth-like margins. Early herbalists regarded this weed as one of the best greens for building up the blood and curing anemia.
Yellow nutsedge (Cyperus esculentus)
Life cycle: perennial herb
Earmarks: plant is distinct yellow-green; stems are triangular with long, grass-like leaves.
Also called northern nutgrass, this is a troublesome weed in the northeastern U.S., competing with crops and reducing the quality and yield in potatoes, corn, tomatoes, beans, and peppers. It spreads easily and reproduces by rhizomes (underground stems), tubers, and seeds. In southern Europe, western Asia, and parts of Africa, it is grown for its edible tubers that taste like almonds, and may be cooked, ground into flour, or made into a cold drink. The species name means edible, and aptly describes this plant. Photo courtesy Robert H. Mohlenbrock
Large crabgrass (Digitaria sanguinalis)
Life cycle: summer annual
Earmarks: grass with a purplish tinge throughout, and has 2-10 fingerlike clusters at the top of the stem.
Also known as finger grass and twitch grass, it was brought from Europe to help provide forage for imported domestic animals. By the late 19th century, farmers had abandoned the plant and replaced it with such profitable crops as corn and wheat. Since then, it has spread throughout most of the U.S. and become a very troublesome weed.
Henbit (Lamium amplexicaule)
Life cycle: winter annual
Earmarks: square stems, opposite leaves, and pink flowers with purple spots.
Purple deadnettle (Lamium purpureum)
Life cycle: winter annual
Earmarks: upper leaves are opposite, short-stalked, heart-shaped, and scalloped along the margins. The lower leaves are similar but are on long stalks.
Hairy galinsoga (Galinsoga quadriradiata)
Life cycle: summer annual
Earmarks: plant is densely covered with white hairs. Tiny, white daisy-like flower heads that have a yellow center.
Hairy galinsoga is especially troublesome in low-growing vegetable crops.
Yellow wood sorrel (Oxalis stricta)
Life cycle: perennial herb
Earmarks: plant forms mats; leaflets are grouped in threes and notched at the tips with yellow flowers.
Children call this plant pickles because the young green fruits and leaves taste sour. Sometimes called sourgrass, the wood sorrels are used as a folk remedy in Europe, Asia, and North America for the treatment of cancer. They also yield an orange dye.
CONTROLLING WEEDS
Controlling weeds in home flower gardens and lawns can sometimes be more challenging than crop fields, according to J.D. Green, an Extension weed scientist with the University of Kentucky Cooperative Extension Service.
“Home areas tend to be in small or enclosed spaces, and they contain a diverse mix of desirable flowers/ornamental species growing in the landscape,” he says. “Therefore, mechanical control efforts (hoeing or hand weeding) and/or mulching are often the best weed control tactics to consider.”
Green says that a key component of any good weed-control program is to first understand the emergence, growth, and reproduction methods of the unwanted plants.
“In the case of most annuals, it is important to destroy the weedy plant before they are able to produce flowers and new seed,” he says. “This greatly minimizes their effort to reproduce. However, this practice must be repeated often since many weedy plants are prolific seed producers, and the seed may germinate for several years after it’s produced.”
Although hoeing or hand weeding can be time-consuming, Green notes that it can also be a good leisure activity—depending on your perspective. “Doing this frequently when weedy plants are still small can be less difficult than dealing with larger mature plants,” he says.
“Good mulching practices can also be quite effective for smoothing some weed problems, but can also provide a desirable environment for the germination of other unwanted plants, depending on the type of mulch used (mulches high in organic matter make good seed beds for germination of weed seeds).”
More specific information for weed control in home landscapes can be obtained from the Kentucky Cooperative Extension Office located in your county.
Herbicides for gardens
Chemical options are limited because of the diversity of plant material in the landscape, according to Green, who notes that it is difficult to produce a herbicide that can control multiple weed species and not cause injury to the desirable plants. There are some chemical options.
Tifluralin (brand product example: Preen)
These soil-applied herbicides are labeled for use on flower beds. There may be others available for commercial applicators. These products are typically recommended for application on established flowers or transplanted flowers. Consult the label to determine which flowers or ornamentals they can be used with.
These products must be applied before weeds germinate; therefore, correct timing of the application must be considered. With soil-applied herbicides, if you see weed problems in the flower bed, it is probably too late unless you kill the undesirable weeds first.
Glufosinate (brand product example: Finale) or product containing glyphosate (brand product example: ROUNDUP)
These non-selective post-emergence herbicides will kill desirable plants if they come in contact with the desirable vegetation. Therefore, to use these products the unwanted plants must be actively growing. You must use extreme caution to avoid contact with the foliage of desirable plants. A product containing glyphosate is very useful to suppress growth of weeds such as Bermuda grass and white clover in flower beds.
Halosulfuron (brand product example: Manage)
This herbicide is effective for specific control of yellow nutsedge; however, the availability of Manage may be limited to commercial applicators since it is used at very low application rates.
Controlling weeds in lawns
Many of the same principles apply to lawns.
“One of the primary weed-control concepts I try to promote for lawn weed control is use of overall good turf-management practices that will help prevent and suppress growth of unwanted weeds and promote and enhance growth of desirable turf grasses,” Green says. “Maintaining a good, healthy turf helps prevent germination of many annual weed species, such as chickweed or henbit during the fall and early winter months, and crabgrass or foxtails in the spring. Good lawn-management practices include maintaining proper pH and soil fertility levels that promote growth of desirable grasses, and adjusting the mowing height to prevent scalping of the turf close to the ground. A closely mowed turf allows light to penetrate the soil surface and trigger weed seed germination.”
Herbicide options to control grasses are much more limited because it is difficult to selectively control grass-type weeds in desirable grass turf, according to Green. The most popular and effective products are herbicides that are applied to the soil surface before weeds germinate. Specifically, they are used for control of plants such as crabgrass. To get the most benefit, apply pre-emergent herbicides in the spring (March to early April) before crabgrass germinates.
One problem weed is yellow nutsedge, a perennial. Green says this weed is best controlled with a herbicide product containing halosulfuron (such as Manage). However, this herbicide may require application by a commercial applicator.
And what about those dandelions?
“We get all excited about weed problems in the spring, particularly when dandelions start to bloom. They trigger our consciousness about weed control. But fall is a better time to think about controlling them. In the spring, they spend most of their energy producing flowers and new seeds. After they flower in the summer and fall, they start building back their root reserves. Therefore, if you treat them in the fall with a herbicide, you get more movement of the herbicide to the root system and this can give you better results.”
CREATIVE USE OF WEEDS
If you have received a professionally designed flower arrangement lately, you may have noticed plants that you hadn’t seen before. These “new flowers” are what many consider weeds, but since they are colorful and interesting, they make exciting additions to the more traditional roses, mums, and lilies.
At Stems & Thee Floral Designers in Bowling Green, owner Jared Chedester uses a lot of plants that would be considered untraditional in flower arrangements.
“We don’t refer to them as weeds,” Chedester says. “We just look at the natural aesthetic beauty of the plant and how it comes into play with the items we’re using.”
Chedester says they use a lot of Hypericum fruit, commonly known as St. John’s wort, because of its beauty and because when it gets warm it smells like coffee. He also uses thistles.
