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Weeds can be the most challenging lawn pests of all.

Image of a sapling tree growing from the gap between asphalt and a building with the caption "weeds are just plants in the wrong place"
Photo by J. Gangloff-Kaufmann

Every plant is native to an ecosystem somewhere in the world. But when a plant is introduced to a foreign ecosystem it may thrive, reproduce quickly and compete with native plant species for nutrients, water and space. The foreign plant becomes a weed. Weeds are serious competitors with lawn grasses, which are also not native to the Northeastern US. Lawn grasses (with the exception of zoysia grass) are much less hardy than weeds and need more care.

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Weedy plant species usually do well in poor conditions like dry, compacted or acidic soils where lawn grasses struggle. Poor conditions may be the reason your lawn is full of weeds. Typical lawn care relies on weed killers (herbicides) to suppress weeds, but if poor conditions are not fixed, the battle against weeds will become a never-ending cycle. Herbicides can leach through Long Island's sandy soil into ground water or move laterally over land to pollute bodies of water, like the Long Island Sound.

What can I do about lawn weeds?

There are several techniques that can reduce weed abundance in your lawn.

Hand weeding is probably the most time-consuming weed control strategy of

Before and after removing a weed with a long taproot
Photos by J. Gangloff-Kaufmann

all. For the very dedicated, it might be an acceptable, if not enjoyable, gardening task. For others, not so much. However, hand-pulling the big weeds like dandelions, thistles (wear heavy gloves!) or broadleaf dock that tend to have hefty, long taproots is worth the time. Using a shovel or a pitchfork to loosen the soil will help free the long taproot so the weed does not grow back. Pulling weeds before they set seed can help lower weed pressure next year. Herbicides can help but often do an incomplete job. When herbicides are used on hard surfaces (driveway and walkway) and dead plants are left behind, they eventually decompose and create soil that encourages more weed seed germination. 

Correcting poor soil conditions is the long-term strategy that helps make your lawn grass healthier and more competitive with weeds. Compacted or dense, hard soils can be improved with aeration and the addition of organic matter. Lawn aerating machines can be rented, but they may be too large and heavy for many to transport. Consider hiring a landscape company to aerate or use a hand aerator. It may take more time, but hand aerators are inexpensive. Organic matter, such as composted manure, should be added after aeration.     

Mowing higher will help your lawn grasses compete with weeds forChart showing why one should mow grasses on a high setting and only cut one third of the blades off. sunlight and space, while allowing the roots to grow deeper. The best guideline for mowing is to remove only a third of the height of the grass blade. This reduces plant stress and water-loss, but also reduces the number of times you need to mow each season if you mow high. For example, if you mow your grass down to a height of 2 inches, you need to mow each time it reaches 3 inches to follow the one-third rule. If you mow to a height of 4 inches, you wouldn't need to mow the grass until it is 6 inches tall, saving you time and gas. Taller grass is healthier and crowds out weeds.

whorls of long fine grass
Whorls of long grass can be an attractive alternative. Photo: J. Gangloff-Kaufmann

Mowing much higher or creating a "no-mow" lawn has gained popularity in recent years as a sustainable alternative to a typical lawn that is mowed weekly. A low input and low maintenance lawn can appear luxurious when the right types of grasses are allowed to grow to their full length. Varieties of fine fescues (Hard, Sheep, Creeping Red fescues) develop into a soft flowing carpet of grass. No-mow lawns aren't completely maintenance-free and will need to be mowed at least once in the early summer to remove seed heads and raked in early spring to remove leaves and debris. 

Herbicides - Lawn care herbicides have been in use for about 70 years. The potential risks to people, pets, pollinators and ground water might make you rethink their use. If your lawn has been treated for years with herbicides or "weed-and-feed" products it can be challenging to reduce or eliminate them. Use products wisely, sparingly, and never let them end up on hard surfaces, like your driveway. Granules of lawn products left on the sidewalk or driveway often get washed away into storm drains, where they end up in streams, lakes or marine ecosystems like Long Island Sound. Overuse of herbicides may allow them to leach through our sandy soils into fresh water aquifers.

  • Synthetic herbicides may be selective (works only on broadleaf plants, not grasses), non-selective (kills everything) or pre-emergent (prevents germination of seeds). Most synthetic herbicides inhibit or disrupt plant growth.
  • Alternative and organic herbicides, like those with vinegar (acetic acid) or essential oils, may have "burn down" activity, which means they destroy plant leaves, but not the roots. They are non-selective and best used in a targeted application (applied only to the undesired plant).

As always, READ THE LABEL on any weed control product and follow those instructions carefully. Many herbicides have requirements for what protective clothing is needed for application and what weather conditions are best for application.

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Common lawn weeds (click on weed names for more information)

Dandelions 

a dandelion plant in a lawn with three yellow flowers
Dandelion flowers. Photo: School of Integrative Plant Science (SIPS), Cornell University.

This rugged and variable plant is among the earliest flowering weeds because dandelions do not die in the winter. Their thick taproot keeps the plant nourished and ready to flower, even in January. While many herbicides are labeled to kill dandelions, they often don’t fully kill mature plants. Hand removal can be a more permanent solution. However, since many bees rely on the earliest flowering plants, you might choose to leave a few in place, at least in early spring.

Crabgrass

a crabgrass plant in between patio flagstone pieces
Large crabgrass. Photo: J. Gangloff-Kaufmann

Unsightly and usually a much lighter color than turf grasses, crabgrass stands out as one of the most common and frustrating weeds of the lawn and garden. It can remain low growing when mowed regularly or stand 2 feet tall in unmowed areas. The flowering stems release thousands of seeds in mid-summer that can last more than 3 years in the soil. Crabgrass is an annual, meaning the plants die at the end of the season and seeds germinate the following spring.  Controlling crabgrass before it sets seed can reduce the number of future sprouts.

Dozens of white clover flowers in healthy grass
White clover can become abundant in poor soils. Photo: J. Gangloff-Kaufmann

White clover

Clovers belong to the legume family, which includes beans, peas, alfalfa and many other familiar plants. Legumes can draw nitrogen from the air and convert it to a type that is available to plants as fertilizer - a unique super power! The beauty of clover flowers combined with an increase in soil fertility has resulted in deliberate use of clover seeds in lawn seed mixtures. White clover is common in lawns with acidic, low fertility and compacted soils. Improving soil conditions and increasing mowing height can help reduce white clover dominance. Since the flowers are so attractive to bees, it is wise to mow flowers before using any product that might harm pollinators. 

a rosette of roundish leaves with seed heads sitting in mulched soil
Broadleaf plantain will grow in most soil conditions. Photo: SIPS, Cornell University.

Broadleaf Plantain

Native to Europe and Asia, this perennial plant is very common and thrives in compacted and disturbed soils, especially in areas with lots of foot traffic. Despite its weed status, broadleaf plantain's leaves and seeds are nutritious and the plant contains useful medicinal compounds. Hand-pulling with a weed tool before seeds are set will help reduce plants and future seedlings.

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Other common weeds of lawns and gardens

Birdsfoot trefoil

plant with small lobed leaves and yellow flowers close to the ground
SIPS, Cornell University

Black medic

Plant with lobed leaves and yellow flowers, close to the ground
SIPS, Cornell University

Bull thistle

Rosette of spiny thistle leaves, flat on the ground
SIPS, Cornell University

Ground ivy

Plant with small leaves and purple flowers
SIPS, Cornell University

Red clover

Clover plant with light purple flowers
SIPS, Cornell University

Smartweed

Tall lanky plant with a spike of tiny pink flowers
SIPS, Cornell University

Virginia creeper

Vine-like plant with five-lobed leaves on the ground
SIPS, Cornell University

Yarrow

Green plant with feathery leaves
SIPS, Cornell University

Yellow nutsedge

Lawn grass with light green blades of nutsedge
SIPS, Cornell University

Do you have a weed you would like to identify and know more about? See the Turfgrass and Landscape Weed ID page.

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