How to Kill Weeds That Grow in Your Yard

Japanese knotweed in bloom.

Toshihiko Watanabe / Getty Images

Eradicating weeds takes time and patience, and you'll need both to get the job done. While most weeds aren't dangerous to the gardener, others can be quite toxic. Pulling entrenched dandelion roots out of the ground can result in a pulled muscle but poison ivy can cause severe allergic reactions.

Tip

It will be easier to remove any type of weed at the root if you first wet the soil.

Here are the best ways to kill or at least slow the growth of seven common weeds, along with tips on what to avoid when trying to gain control of your yard.

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Killing Dandelions

One of the essential things to know about the dandelion (Taraxacum officinale) is that this common lawn weed is a perennial. Since they're perennials, they maintain a permanent base camp on your lawn until you remove them entirely.

Dandelions in the lawn are difficult to control because of their long taproot. The following three ways of killing dandelions DO NOT WORK because of that taproot:

  • Pulling off the top part of the plant leaving the root behind quickly producing another yellow flower.
  • Spraying around the dandelion with a weed killer specifically for use on a lawn; the leaves will die, but the root will still be left behind.
  • Using a product that's a combination of weed killer and lawn fertilizer; it won't reach the taproot and the dandelion will survive.

Instead, you can use a non-selective herbicide, such as vinegar, but the downside is that it will leave dead spots all over your lawn where the grass around the dandelion is also killed. The very best approach to permanently killing these weeds and sparing the grass is a two-step approach:

  1. Lift the dandelion off its root with a weed digger (an inexpensive fork-like tool).
  2. Spray a small amount (less than a teaspoon) of a weed killer that is designated for use on a lawn down into the small hole left after lifting the dandelion. This technique will kill the taproot without damaging the grass.

Removing Crabgrass

You'll need a different method to kill an annual weed, such as crabgrass (Digitaria). Crabgrass starts its invasion anew each year. You could, theoretically, eradicate crabgrass in the spring by using a pre-emergent herbicide, assuming you get the timing correct. But, if you fail to eradicate this weed in the spring, you'll have to wait and use post-emergent crabgrass killers on it in summer.

Tip

Toxin-free corn gluten meal may be an antidote for crabgrass (and possibly dandelions). It also works as a good lawn fertilizer while also acting like a herbicide that prevents weeds from sprouting.

Eliminating Poison Ivy

Poison ivy (Toxicodendron radicans) is another cunning weed that most homeowners will agree that a property is better off without. Proper identification of the poison ivy in your yard should precede any efforts to eradicate it. You must be careful when removing poison ivy.

Once you remove poison ivy, you need to meticulously dispose of the weed. It's important to note that poison ivy emits a toxin, urushiol, that remains active for up to five years, even on dead plants, its sap, and on anything else that brushes up against it. Follow these three critical pointers on how to avoid urushiol:

  1. Never burn a pile of brush or plantings that contain poison ivy; smoke releases urushiol into the air and can cause respiratory health issues.
  2. Bag the poison ivy and roots in heavy-duty plastic garbage bags and secure it so there's no accidental brushing up against the plant, even if it's dead.
  3. After weeding poison ivy, wash your clothing in hot water with a degreasing detergent and clean non-cloth items with hot water and strong dish detergent.

Smothering Japanese Knotweed

Many homeowners share a yard with the invasive Japanese knotweed (Polygonum cuspidatum), but though it's common, it's tough to identify. Once you know what it is, cutting down a swath of it won't eliminate the problem. Either the root ball will continue sending up new shoots, or your efforts to dig out the roots will leave a little rhizome behind resulting in the sprouting of more knotweed shoots.

This is one weed that needs to be removed using a glyphosate-based herbicide. However, if you're willing to put in the extra work, you can eventually beat Japanese knotweed by smothering it with tarps by cutting off the sun and water it needs to grow.

Slowing Down Oriental Bittersweet

Another challenging weed is Oriental bittersweet (Celastrus orbiculatus). You can try to eliminate it by putting in a lot of effort to pull and cut it, or you can moderate its growth with another method. To cut off its supply of nutrients and to keep the weed from smothering trees it grows around, simply cut the thickest vines from ground level to your waist. The method won't kill the bittersweet weed, but it will slow it down enough to save your trees.

Clearing Out Pretty Weeds: Moss and Wild Violets

You may appreciate certain weeds, such as moss and wild violets. Some gardeners even cultivate moss plants as an alternative to grass lawns and consider wild violets as wildflowers.

But if you wish to kill the moss in your lawn, it helps to learn more about why it's growing in your yard in the first place. It may be an indication of deeper soil problems, such as poor drainage and circulation, low soil fertility, and unbalanced levels of pH. Learn how to fix the problems and you'll be able to kill these weeds permanently.

Though wild violets (Viola spp.) may appeal to some, you may want to eliminate these purple or white dots from your lawn. Spray the violets in autumn with a triclopyr-based herbicide.

Article Sources
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  1. Dandelions. West Virginia Extension Service

  2. "Corn Gluten For Crabgrass Control". University Of Maryland Extension, https://extension.umd.edu/resource/corn-gluten-crabgrass-control.

  3. "Poisonous Plants - Types Of Exposure | NIOSH | CDC". CDC, 2018, https://www.cdc.gov/niosh/topics/plants/exposure.html.

  4. Glyphosate General Fact Sheet. National Pesticide Information Center

  5. Triclopyr. National Pesticide Information Center