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Ironweed Management: Tips On Controlling Ironweed Plants

Ironweed Management: Tips On Controlling Ironweed Plants


By: Bonnie L. Grant, Certified Urban Agriculturist

Ironweed is an appropriately named plant. This perennial flowering native is one tough cookie. Controlling ironweed plants has been equated with nuking a fortified bunker. This may sound discouraging but consistent mechanical management and post-emergent herbicides are effective ironweed management. A few tips on how to kill ironweed should get you on your way to controlling this pest of the field.

Is Ironweed Invasive?

Ironweed establishes in neglected and disturbed areas. It is common throughout the United States, especially in the central prairies. This herbaceous plant produces multiple branches and bright purple flowers. Once mature, ironweed can grow 10 feet (3 m.) in height with densely fibrous taproots and rhizomes. The entrenched rooting system makes hand pulling nearly impossible and leaving any part of the root behind will result in regrowth. In large fields, herbicides combined with mowing are the recommended methods to ironweed plant control.

Ironweed is one of the most common problem plants found in pastures across the American central and southern zones. The largest variety, tall ironweed, can produce over 14,000 seeds in a season. Combine this aptitude with the tenacious root system and you have one persistent plant. In unmanaged settings, ironweed can spread and out-compete native plants. Early detection can help prevent rampant colonizing. Timing of treatments also affects the success of controlling ironweed plants. A two-pronged assault is necessary to get a handle on this stubborn pest plant.

Mechanical Ironweed Plant Control

Early mowing followed by a subsequent mowing a month later has been shown to give the greatest control. Mowing by late May to early June followed by mechanical intervention when plants are 6 to 8 inches (15 to 20 cm.) tall can reduce up to 87 percent of the population.

Many gardeners with natural stands of wild forbs actually prefer to let the weeds form their lovely flowers, which attract butterflies and bees. The plants are then mowed in fall to prepare the field for winter dormancy. Plants will re-sprout in spring. In areas, where the plant is a nuisance, however, it is important to mow before any flowers are spotted to prevent seeds.

How to Kill Ironweed

Unfortunately, for those of us who prefer not to use chemicals in our land, complete ironweed management can’t be achieved without herbicides. You can mechanically reduce a stand with consistent mowing but the roots will still be viable in soil, ready to produce more stems.

Recommended treatment programs state that chemical control can take 12 to 18 months for total success. Mow early and wait for the plants to grow back. The young leaves will be particularly susceptible to foliar herbicide applications. Suggested chemical formulas should include glyphosate, dicamba, 2,4D, or triclopyr. Use all cautions and application rates recommended by the manufacturer.

One application is not sufficient to kill ironweed. Mid-summer application once mowed weeds have grown back will severely deplete plant health,, but because seed stays viable in soil for many years, the following spring may see another crop of new plants. It is therefore, necessary to repeat the process the following year.

The new crop shouldn’t be as thick as the initial population and hand spraying is usually sufficient to pick up individual plants. Broadcast spraying is not recommended where clover and other broadleaf plants are desired. Ironweed management is an ongoing process in many regions. Consistent control is usually necessary in subsequent years.

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How to Remove Japanese Knotweed

The Spruce / Jordan Provost

Japanese knotweed (Polygonum cuspidatum)—nicknamed Godzilla weed—is one of the world's most invasive plants.   If you've ever attempted to eradicate this weed, you already know of its Godzilla-like qualities. Japanese knotweed is so tenacious that it has been known to grow through solid masonry foundations. There are several approaches you can use to get rid of this plant, and it sometimes requires multiple attacks for complete eradication.

What Is Japanese Knotweed?

Japanese knotweed is a herbaceous perennial plant, meaning it dies back into the ground for winter before sprouting anew in the spring. It can grow between 3 feet and 8 feet tall on average with a bushy appearance. Its leaves are a medium green color, and it sports small white-green flowers in the late summer.


Kill Weeds With Heat

Our early ancestors discovered fire and invented gardening. And even though farmers for centuries have used controlled burning to improve crops, it has not been until recently that home gardeners began to use mechanical flame torches, or flamers, in the garden. Of course, it's never too late to invent a garden tool that kills unwanted weeds without requiring the gardener to bend and pull, disturb the soil, or lace both soil and crops with herbicides.

Though flaming technology has been around since the 1940s, home gardeners have expressed renewed interest in these weed-fighting tools. Flamers require no chemicals, and don't result in groundwater contamination or chemical residues on garden crops. But safety concerns of another type remain. Never use flame torches around any dry, brown, or otherwise flammable material. Also, their use during dry periods in forested or arid regions is prohibited, or ought to be. Always check with your local fire department or town clerk before investing in a flamer.

Personal safety is another issue. These portable torches use pressurized tanks of propane and, if handled carelessly, can be hazardous. When operated properly, however, flamers are easy-to-use, safe, and timesaving gardening tools.

Flamers are portable gas torches that produce intense heat (about 2,000°F). When you pass the flame over and around weeds, it quickly boils the water in the plants' cells, causing them to burst. Once the heat destroys any section of a weed's stem, for instance, water and nutrients cannot reach the leaves, and the top part of the weed dies.

For the home gardener, killing weeds is as easy as holding the flamer and walking slowly (1 to 2 miles an hour) between garden rows. Killing a weed requires heat for only 1/10 of a second.

"You know you're successful when the weed changes from a glossy to a matte finish," says Tom Lanine, weed ecologist at the University of California at Davis. "The weed may not droop immediately but will wilt and die within a few hours. Then you just leave the weed to compost naturally. You don't want to disturb the soil and bring more weed seeds to the top."

For effective weed control, use flamers in spring and early summer as annual and perennial weeds emerge. Killing larger, mature plants requires more heat, so save time and fuel by flaming weeds when they're still young and tender.

For effective control, Penn State vegetable specialist Mike Orzolek recommends a series of flaming attempts, 2 to 3 weeks apart. Flaming kills annual weeds completely (though more annual weeds will pop up), but it doesn't kill the roots of perennial weeds. These will send up new shoots within a week or so after flaming. Additional treatments will eventually deplete the roots' stored energy, and the weeds will die.

Lanine and Orzolek both recommend using flamers as a pre-emergence control. Most viable annual weed seeds are in the top 1/4 inch of soil, and flamers can kill already-germinated seeds with heat.

Lanine recommends watering the soil before applying heat. "Unless the seeds have sprouted, there's no way to kill them with flamers. Even when they've sprouted, the soil is an incredible insulator," he says. "However, if the soil is saturated with water, then you will get some conduction of heat and can kill some seedlings in the soil."

Buying Tips: Features to Consider

Flamers are long metal tubes that carry gas to the flaming tip. The function sounds simple enough, but some products have features that make weeding both easier and safer.

Flamers are available in garden centers and in many gardening and homeowner catalogs. Expect to pay $50 to $90 for a flamer, which should include an extension hose and gas regulator. The gas tank and propane are sold separately. A 5-gallon (20-pound) tank costs about $20 to $25 in hardware stores, and fuel will be about a dollar a gallon.

For a flame that starts safely and easily, look for one that has an ignition switch. These devices send a spark directly into the torch. You simply turn on the gas, hit the switch, and you're on your way. Not all flamers are that easy to start, though. Many manufacturers provide flame-starting tools that you must hold near the gas outlet. These devices generate sparks that ignite the gas. They are simple and safe when used properly. Don't use matches because your hands will be too close to the flame when it ignites.

Some flamers attach directly to small propane tanks (14 to 16 ounces). This makes them easier to maneuver, but they burn for only 1 to 1 1/2 hours. Flamers attached to large tanks (like those used with barbecue grills) need an extension hose, that runs from the tank to the flamer. The hose length limits your range, however, and you must lug the tank around. Use a dolly if the tank is too heavy to move around comfortably, but make sure you strap the tank down securely.

Most flamers include valves that allow you to adjust the flame from low to high settings. How much fuel you use will depend on the size of the burning tip and your flame-adjustment setting. Typically, a 5-gallon gas tank will provide enough for 3 to 6 hours of burning. However, a flamer with a 3-inch tip at full throttle will burn 20 pounds of fuel (about 5 gallons) in an hour.

The Size of the Burning Tip

Tip size is important, and you should consider the type of weeding you want to do. For example, if you'll be working in tight spaces, you'll have much better control using a torch with a tip (burning end) that produces a fine flame. Remember, a 2,000°F flame will kill prized garden plants just as easily as it will kill unwanted weeds. If you need to manage heavy weed growth over a large area, buy a flamer with a 1 1/2- to 3-inch-diameter tip. Flamers with these tips, sometimes called torch bells, send out a wider flame band than other models, allowing you to cover more area in less time. For most home gardeners, flamers with 3/4- to 1 1/2-inch tips are best.

When used properly, flamers provide effective weed control.

Here are a few important safety tips:

  • Never flame weeds during extremely dry periods. Flamers produce intense heat even wet mulch will ignite. Don't flame if you have any debris around and as little as a 3- to 5-mile-per-hour wind.
  • If you're using a flamer with an extension hose, keep the flame away from both hose and tank.
  • Though the flamer's handle doesn't get hot, the flaming tip does. Even after turning off the flame, keep the flamer away from people and combustible materials.
  • Always be cautious when lighting the flamer. Follow the manufacturer's instructions exactly.

Dan Hickey is a former editor of National Gardening.


Prairie history

Prairies are divided or classified by height, which is determined by yearly rainfall.

  • In the eastern part of the Midwest, including Minnesota, is the tallgrass prairie.
  • Further west is the mid-grass prairie.
  • On the western edge, in Colorado, is the shortgrass prairie.

Prairies were once dominant from Ontario south to Texas, and from Colorado and Montana east to Indiana.

  • In Minnesota, tallgrass prairies thrived in the southern and western parts of the state, while pine and spruce coniferous forest dominated the north and northeast.
  • Maple and basswood deciduous forests covered most of the east central and southeastern part of the state.

Planting a residential or prairie garden

Select a site with the following specifications:

On the east, west or south side of buildings.

Does not contain weedy vegetation such as quackgrass, Canada thistle, reed canary grass.

Seek professional help for preparing such a site.

To avoid fire danger:

Locate the prairie at least 30 feet from buildings.

Separate the prairie from buildings with an area of gravel, concrete, turfgrass or irrigated plantings.

Prune live and dead branches of nearby trees at least ten feet above the ground.

Site design

  • Check with your local city government about local weed ordinances before developing a prairie. You may need to apply for variances.
  • Some prairies look more natural than other landscapes. Discuss the prairie with neighbors to let them know about the changes you are making and that the site is being maintained.
  • Consider using mowed edges, signs, bird houses and edging fences near your prairie to show the area is meant to be there.

Soil analysis

Prairie plants are adapted to specific soil types and moisture levels. Understand the drainage and sun and shade exposure of your site when selecting plants for your location.

Determine whether you have sandy, clay or loamy soil.

Have your soil tested at the University of Minnesota Soil Testing Lab to determine the soil pH and organic matter.

Determine the soil moisture of your site.

Dry - draining readily with no standing water.

Mesic - medium moisture with some puddles after rain.

Wet - wet soil throughout the season with standing water in spring and fall.

Standing water or water that does not drain from a 1-foot-deep hole within 24 hours are indicators of wet and poorly drained soils.

Remove all existing plants to reduce plant competition. New prairie seedlings are not able to establish if they are competing with existing vegetation. Weeds and turfgrasses must be removed. Seed must have good contact with soil for germination.

Three methods to establish a prairie in an existing lawn or area of other vegetation:

  • The most common method of establishment uses a nonselective herbicide containing the active ingredient glyphosate to kill all existing vegetation. Follow directions carefully and wear protective gear.
    • Wait 1 to 2 weeks after applying glyphosate. When existing vegetation has died, the soil should be tilled to a depth of 12 inches or more with a rototiller, harrow or disc to incorporate dead material.
    • If a seed drill or slit seeder will be used in planting, tilling may be eliminated and the now dead vegetation mowed to a 1- to 2-inch stubble.
    • After tilling, the site should be raked, either by hand or with a power rake.

CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.

  • Put a dark plastic sheet, tarp or pieces of plywood over the grass for at least two months before you begin planting.
    • All plants will be killed and can be removed. It may be difficult to remove tough perennial weeds like thistles and quackgrass.
    • Once the vegetation is dead, till the area thoroughly.
    • This method works best when begun in the summer or fall to prepare for a spring planting.
  • Turn the soil and cultivate the area every few weeks for a complete growing season.
    • Turning the soil brings weed seeds to the surface, and cultivating kills the seeds that have germinated since the soil was last turned.
    • Till to a depth of 12 inches or more and rake the area to create a uniform fine seedbed.

Select plants that will grow well in the sun, shade, soil type and moisture of your particular site.

Prairies consist of 80 percent grasses and sedges and 20 percent wildflowers or forbs. Include a mixture of warm-season and cool-season grasses.

Warm-season grasses predominate in prairies. They are slow to grow in the spring but tolerate summer heat and drought and flower in the late summer and fall.

Cool-season grasses grow in early spring and fall but are often dormant in summer.

Grasses provide physical support, weed competition, protection for wildflowers and a source of food and shelter for birds during the winter.

A "nurse grass" that germinates quickly may be planted to minimize weed competition during establishment.

Wildflowers should be selected based on soil moisture and available sunlight and should include a variety of bloom times to support native insects and butterflies.

Seeds vs. plants

You can start a prairie from seeds or plants. Plants can be used for small areas, however larger areas will require seed for establishment.

Starting from seed is more economical, but can take two to five years for the plants to reach full size.

Plants are more expensive, but establish quickly and may flower the first year. Plants can be planted anytime from spring through fall.

Some species are available only as live plants.

Prairie seed companies create seed mixes appropriate to your site conditions.

Consult with local seed dealers to determine the correct mixtures and amounts.

Be sure that any seeds you purchase are packaged for the year that you will sow them and list current germination and pure live seed percentages.

"Seed-in-a-can" wildflower mixes are not recommended as they often contain annual plants and a mixture of seed for all soil types.

Group several plants of the same species together to make a showy display and to increase pollination and seed set.

Common prairie wildflowers

Name Flower color Flowering date Height
Big bluestem (Andropogon gerardii) Bronze with bluish stems Aug. - Sept 3-8'
Butterfly weed (Asclepias tuberosa) Orange-red July - Aug. 1-2'
Blue false indigo (Baptisia australis) Blue June - July 2-5'
Purple coneflower (Echinacea purpurea) Purple June - Sept. 2-4'
Oxeye (Helianthus helianthoides) Yellow July-Sept. 3-4’
Meadow blazing star (Liatris pycnostachya) Purple Aug. - Sept. 2-4'
Hoary puccoon (Lithospermum canescens) Orange May - June 1-2'
Wild lupine (Lupinus perennis) Blue May - June 1-2'
Large-flowered beardtongue (Penstemon grandiflorus) Pink/purple May - June 2-3'
Prairie phlox (Phlox pilosa) Pink/purple May - July 1-3'
Grey-headed coneflower (Ratibida pinnata) Yellow July - Sept. 3-6'
Black-eyed Susan (Rudbeckia hirta) Yellow July - Aug. 2-3'
Little bluestem (Schizachyrium scoparium) White with bluish foliage Aug. - Sept. 2-4'
Cup plant (Silphium perfoliatum) Yellow Aug.-Oct. 3-7’

Common prairie grasses

Name Flower color Flowering date Height
Sideoats grama (Bouteloua curtipendula) Orange-purple July - Sept. 1-3'
Blue grama (Bouteloua gracilis) Tan with green stems July-Sept. 18-30”
Canada wildrye (Elymus canadensis) Tan with green stems June-Sept. 3-4”
Switchgrass (Panicum virgatum) Red, purple and tan flowers July-Sept. 3-6’
Indian grass (Sorghastrum nutans) Golden-brown Aug. - Sept. 3-6'

Planting grasses

The best time to sow seed is in the spring between May 15 and June 20. Seed may also be sown in fall, between mid-October and freezing.

Even seed distribution and good seed-to-soil contact are essential.

Seed may be broadcast by hand:

Mix seed with slightly damp sawdust or peat moss as a carrier.

Use one bushel of carrier per 1000 sq. ft. of area.

Distribute seed in a broad arc to spread evenly.

Mix seed with clean sand or vermiculite.

Make passes in two different directions.

For larger areas, mechanical planters can be used, including:

Tye drill, Truax drill, Rangeland drill.

After sowing, roll seed to improve soil-to-seed contact. Be sure to roll when soil is dry.

Planting wildflowers

Wildflowers may be sown with grasses or planted one to two years after grasses have been sown.

Wildflowers are generally sown from seed on larger sites, as this is most economical. Plants will take two to five years to establish and bloom.

Wildflower seedlings may be planted also. Transplants are more expensive, but establish and bloom quickly.

Wildflowers may be clustered near paths and residences for best color in these areas.

Seeding rates

Seeding rate varies by species and seed quality.

A general rule of thumb is 30 seeds per square foot.

Grasses may be sown as low as 20 seeds per square foot.

Forbs or wildflowers as high as 60 seeds per square foot.

Consult information on the label for each type of seed you are planting.

Hand sowing for small sites may require more seed.

Get more specific instructions on seeding rates from the information provided when buying seeds.

Watering after seeding improves germination, but is not essential unless no rainfall occurs for several weeks.

  • Cover with a thin mulch of clean, weed-free straw to prevent drying, reduce exposure to wind and animals and to prevent erosion on slopes.
  • Prairies usually do not need herbicides, fungicides, insecticides or fertilizers.
  • Weed control in the first two years of a prairie is essential.
    • Hand weeding, burning and mowing are the most effective ways to control weeds.
    • Remove woody plants, such as tree seedlings.
    • Any weeds that are allowed to go to seed will mean more work in the future.
    • Remove weed seed-heads in the first few years to eliminate future problems.

First year management:

Control weeds by mowing regularly in the first year to a height of 4 to 6 inches. Mowing at this height will reduce weed competition without harming new prairie grasses and wildflowers.

Do not allow weeds to go to flower and seed. Ideally all weeds can be mowed or removed to grow no taller than 8 to 12 inches.

Don’t pull weeds by hand as this disturbs new prairie plants and may introduce additional weed seeds.

At the beginning of the second season, evaluate how many weeds are present. It may be necessary to mow the prairie to 4 to 6 inches the second and third year to keep weeds under control.

The goal is to minimize weed and seed set while allowing prairie plants to grow.

Prairie grasses develop roots the first few years and grow slowly above ground.

By the third year, the plants develop more growth above ground.

Long-term management:

After the prairie has been established for at least three years, you can maintain the prairie with controlled burns.

Controlled burns are recommended for larger sites, which are often done on a rotation basis, with 1/3 of the plot mowed annually.

Burning in April or early May is best for native plants.

Check with your local fire department and the Department of Natural Resources to get information and required permits.

On smaller sites, mowing is an alternative to controlled burning.

Mow once a year after prairie seeds have fallen, usually in early spring.

Remove clippings to expose crowns of plants.

For additional help in establishing and maintaining your prairie, consult private restoration or landscaping companies and the Department of Natural Resources.

Mary Meyer, Extension horticulturist and Julie Weisenhorn, Extension educator


Killing with Chemicals

There are many chemicals on the market that tout their weed-killing abilities. These include pre-emergent and post-emergent herbicides. Pre-emergent must be applied before the weed seeds germinate because these prevent that from happening, which keeps the weeds from growing. Post-emergent herbicides kill a weed in a week, but the weed itself remains in place until it eventually shrivels and dies.

This type of herbicide is absorbed through a plant's leaves, and it can be taken up by nearby desirable vegetation if you are not careful in your application. Until the herbicide causes the weed to shrivel and die, it will remain an eyesore in your garden or lawn. Some of these chemicals are also toxic to aquatic life and some mammals, so read the label thoroughly before purchase.


4. Norway Maple (Acer platanoides)

Origin: Europe

(Image by Zelimir Borzan, University of Zagreb, Bugwood.org)

Arrival: The plant explorer John Bartram first introduced the Norway maple to the United States from England in 1756. The widely adaptable tree quickly became popular and was planted in towns as a shade tree and in rural communities.

Impact: The Norway maple displaces native trees and has the potential to dominate a landscape in both the Northeast and Northwest. It displaces native maples like the sugar maple and its dense canopy shades out wildflowers.

Native Alternatives: Sugar maple (Acer saccharum) and red maple (Acer rubrum)


Product Storage and Cleanup

If desired, you can store unused glyphosate 41 in the sprayer, but be sure to release the pressure by unscrewing the top until you hear the pressure release then securely screw the top back in place. You can also transfer any unused herbicide into a plastic container for future use. Once your sprayer is empty, thoroughly wash all parts, including the wand, to remove any herbicide residue. Fill the tank halfway with water, pump up the sprayer and rinse away any glyphosate deposits by spraying the water through the wand onto a paved driveway so it doesn't affect any vegetation. repeat the process. Store the unused herbicide in an area where children and pets can’t get to it or accidentally knock it over.


Watch the video: ironweed foraging and uses