What are weeds?
Weeds are plants that grow where they are not wanted. They compete with desired plants in gardens, lawns, and fields for water, nutrients, sunlight, and space. Common lawn and garden weeds include dandelions, crabgrass, clover, plantain, chickweed, henbit, knotweed, and purslane. Agricultural weeds reduce crop yields and profits for farmers. Some weeds are also invasive plants that can take over native plant communities.
Why get rid of weeds?
There are several reasons to get rid of weeds:
- Weeds compete with desired plants for water, nutrients, and sunlight
- Weeds can harbor insect pests and diseases that may spread to desired plants
- Some weeds produce chemicals that inhibit the growth of other nearby plants (allelopathy)
- Weeds reduce the aesthetic appeal of lawns and gardens with their presence
- Some weeds have thorns or burs that can injure people and pets
- Weeds reduce agricultural yields and profits
- Invasive weeds can displace native plant communities and reduce biodiversity
Controlling weeds allows desired plants like lawn grasses, garden plants, and agricultural crops to thrive better with reduced competition for resources. Weed management improves the appearance of landscapes. Removing weeds also prevents injury from thorns and burs and limits the spread of pests and diseases in lawns and gardens.
Weed control methods
There are several methods available for controlling weeds, but not all permanently remove weeds. Common weed control techniques include:
Mowing and pruning
Mowing and pruning weeds prevents them from flowering and producing seeds. However, it does not kill the roots of perennial weeds, so they will regrow. This method is best for managing annual weeds.
Cultivation and hand weeding
Cultivating the soil with tools like hoes and rakes uproots emerging weed seedlings. Hand weeding also removes weeds by grasping stems close to the roots and pulling up the entire plant. But again, the roots of perennial weeds often remain intact to regrow new plants. Frequent cultivation and hand weeding are required for ongoing management.
Mulching
Applying organic mulch like wood chips, bark, or straw around desired plants smothers weeds by blocking light. 2-4 inches of mulch must be maintained for effective weed control. But mulching does not kill perennial weed roots, so some weeds may still emerge through the mulch layer.
Smothering or solarizing
Layers of opaque material like cardboard, black plastic, or landscape fabric placed over areas of weeds blocks sunlight and smothers plants. For solarization, clear plastic is used to trap heat and kill plants and seeds. Smothering is effective on annual weeds and takes 1-2 growing seasons to manage perennials. Solarization requires several weeks of warm weather to work.
Burning
Using a flame weeder or carefully directed propane torch kills emerging weed seedlings and leafy growth of perennials if done repeatedly, but does not destroy roots of established weeds.
Herbicides
Herbicides (chemical weed killers) provide efficient control by systemically killing the entire weed plant, including the roots. Effectiveness depends on proper herbicide selection, timing, dosage, and application for target weeds. Some herbicides have residual activity that prevents new weeds from germinating. Herbicides may require repeat applications on perennial weeds as roots resprout. Organic herbicides made from plant oils or acids are also available.
Methods for permanent weed removal
While the methods described above help manage and suppress weeds to varying degrees over time, a few techniques can provide more permanent weed removal by killing roots or preventing regrowth:
Tilling
Deep tilling with a rototiller or plow buries weed roots and shoots deep enough to prevent regrowth. Tilling must be repeated routinely to control new weeds from seeds in the soil. This technique is too disruptive for established lawns and garden plantings but can be used to prepare weed-free seedbeds.
Tarps
Heavy duty black plastic or rubber tarps placed over weedy areas for at least one full growing season kills plants and seeds by blocking all sunlight. The edges must be secured down well. This is very effective but also eliminates desired plants covered by the tarp.
Solarization
As described above, solarizing soil under clear plastic during hot, sunny weather kills weed roots and seeds. Temperatures of 115-140°F are needed at 4-8 inch soil depth for 4-6 weeks. Effective in all climates with adequate solar radiation.
Soil sterilization
Heating soil by steam, electricity, or solarization destroys all plants, seeds, and microorganisms. This leaves a sterile growing medium that can be reseeded or replanted. Very effective but energy and labor intensive.
Smothering
Heavy layers of mulch like wood chips (8-12 inches), cardboard covered with wood chips/soil, or dense planting of smother crops like winter rye or sudangrass blocks all sunlight and prevents weed emergence. Must be maintained 1-2 growing seasons.
Combined herbicide applications
Using systemic non-selective herbicides that kill all plant tissue, like glyphosate (Roundup) or glufosinate (Finale), together with a pre-emergent herbicide provides thorough weed control. The systemic herbicide kills existing weeds above and below ground. The residual pre-emergent herbicide prevents new weeds from seeds. This combined approach provides long-term weed prevention but eliminates all existing vegetation.
Permanent weed control methods by situation
The best permanent weed removal strategies depend on the setting. Recommended methods for various situations include:
Garden beds, borders, and planting areas
– Solarization under clear plastic sheets in summer
– Applying thick mulch layers like wood chips, pine needles, or gravel
– Layering cardboard and/or newspaper covered with mulch
– Growing weed-smothering cover crops followed by mulch
Lawns and turf
– Smothering small areas with heavy black plastic for a growing season
– Repeated application of selective and/or non-selective herbicides
– Maintaining a dense, vigorous lawn by proper mowing, fertilization, irrigation, and overseeding
Driveways, walkways, and patios
– Spot application of non-selective, systemic herbicides on emerging weeds
– Using a propane weed torch for emerging weeds
– Maintaining a deep layer of gravel or landscape rock over fabric weed barrier
Agricultural fields and pastures
– Repeated tilling before establishing crops or pasture
– Herbicide application – systemic, non-selective on existing weeds plus pre-emergent residual
– Establishing competitive cover crops before desired crops or forage
– Occasional plowing and reseeding established crops and pastures
Native landscapes and open spaces
– Eliminating invasive weeds through persistent cutting, digging, or herbicide treatments
– Establishing dense plantings of native grasses and wildflowers suited to the site
– Routinely spot treating any emerging or invading weeds
Preventing weeds
While getting rid of existing weeds is important, prevention of new weeds should be part of any long-term weed management plan through the following practices:
- Use weed-free seed mixes when planting lawns, pastures, wildflowers, and crops
- Inspect plants, soil, mulch, and other materials for weed seeds or rhizomes before bringing them onto the property
- Monitor for and remove weeds early before they establish, flower, and produce seeds
- Clean equipment, vehicles, and footwear that may transport weed seeds
- Maintain healthy plantings of desired vegetation that are dense enough to outcompete weeds
- Use pre-emergent herbicides on paths, drives, and planting beds to inhibit weed seeds from germinating
- Mulch beds annually to block light needed for germinating weed seeds
- Scout for and control small weed infestations before they spread
Prevention is much easier than trying to permanently kill established, entrenched weeds. But even with the best practices, weeds happen, so be prepared to take control measures when needed.
Dealing with persistent perennial weeds
Vigorous perennial weeds with extensive root systems pose the biggest challenges for permanent removal. Some of the most notorious include:
Dandelions
Dandelions have a taproot up to 18 inches deep making them difficult to hand pull. Systemic herbicides like glyphosate work well. But pre-emergent herbicides and proper lawn care to avoid bare spots are key for prevention.
Nutsedge
Yellow nutsedge and purple nutsedge produce tubers that resprout year after year. Digging removes most tubers. Herbicides with the active ingredients sulfentrazone, halosulfuron, or bentazon target nutsedge. Use pre-emergent herbicides to prevent nutsedge establishment.
Bindweed
Field bindweed spreads by deep rhizomes and is very hard to eradicate. Persistence is needed – repeated digging and systemic herbicide application for several years. Exclude light with barriers and mulch to weaken infestations.
Quackgrass
Quackgrass is a cool-season grass with extensive rhizomes. Combining tillage to disrupt rhizomes with glyphosate treatments for regrowth provides control. Pre-emergent herbicides also help prevent quackgrass invasion.
Johnsongrass
A warm-season grass spread by rhizomes and seeds, Johnsongrass requires diligence. Integration of tillage, mowing, competitive planting, and herbicides is often needed for full control. Start pre-emergent herbicides early before germination.
Kudzu
The vigorously growing vines of invasive kudzu can be controlled with persistence. Cut vines repeatedly, apply systemic herbicides to regrowth, and use pre-emergent herbicides. Establishing plantings of native grasses and forbs also helps compete against kudzu.
Conclusion
Eliminating weeds permanently requires killing the entire plant including the roots to stop regeneration of new growth. For established perennial weeds, a combination of manual removal, proper soil preparation, competitive plantings, mulching, and judicious use of pre-emergent and systemic herbicides is needed over several growing seasons. For best results, integrate multiple strategies and aim to prevent new weeds alongside managing existing infestations. With diligence and patience, you can achieve a weed-free landscape.
