The Basics of Killing Weeds

If you have a yard, you have weeds. They may lurk in the lawn, thrive under a shrub or flourish in flowerbeds, making weed control a constant battle. Weeds are probably taking root and/or spreading in your yard even as you’re reading this article.

Your best hope in winning the war on weeds is to know your enemy – and the weapons at your disposal. Review this weed-killing glossary to hone your knowledge and arm yourself for the next round of weed wars.

What Is a Weed?

A weed is a plant that’s growing where it’s not wanted. Weeds aren’t something you plant intentionally; they just appear. Often they grow vigorously, outpacing and overrunning desirable plants. There are several types of weeds.

Annual weed: Completes its life cycle – from germination to setting seed – in one growing season; some annual weeds complete their life cycles in a matter of weeks, producing several generations in a single year

Fact: Annual weed seeds can lie dormant in soil from four to 40 years.

Examples: chickweed, crabgrass, lamb’s-quarters, yellow oxalis

Perennial weed: Lives for two or more years; plants grow as long as conditions are favorable and frequently die back to soil level with hard frost; new growth emerges at the start of the growing season, originating from roots or stem remains; in warmer regions, some perennial weeds can be green year-round

Fact: Perennial weeds spread by various means, including seed, stems that root as they creep along or pieces of root.

Examples: creeping charlie, curly dock, dandelion, plantain

Broadleaf weed: Leaves are broad and flat (not grassy or needle-like)

Fact: Broadleaf weeds are easiest to kill or remove when they’re young and actively growing. Some mature broadleaf weeds develop a layer that makes it difficult for weed killers to penetrate.

Examples: chickweed, clover, dandelion, henbit

Grassy weed: Looks and grows in ways that resemble grass; leaves are produced one at a time and look like grass blades

Fact: Many perennial grassy weeds form rhizomes, fleshy roots that resprout if left behind in soil during hand-weeding.

Examples: Bermudagrass, crabgrass, giant foxtail, goose grass, quack grass

Herbicides

A herbicide is a chemical used to kill or inhibit plant growth. Anytime you use a weed killer, you’re using a herbicide. Some herbicides have residual properties, meaning they continue to kill weeds for a specified time period following application. There are several types of herbicides.

Nonselective herbicide: Kills any green and growing plant, whether or not it’s a weed

Selective herbicide: Kills only specific types of growing plants; for example, a selective herbicide may kill broadleaf weeds and not grassy plants, so that you can spray it on broadleaf weeds in a lawn without harming grass

Pre-emergent herbicide: Prevents seeds from germinating or kills germinating seeds before seedlings emerge from soil; must be applied before weed seeds germinate

Post-emergent herbicide: Kills existing weeds that are actively growing; two types: contact and systemic

  • Contact herbicide – only kills the plant parts the chemical touches; ideal for treating annuals and perennial weed seedlings
  • Systemic herbicide – absorbed by leaves, stems or roots of a plant and moves throughout the plant, affecting every part; effective on annuals and established perennial weeds; must be applied when weeds are actively growing

To control some especially challenging weeds, like nutsedge, clover, creeping charlie or Bermudagrass, you’ll want to choose a specific herbicide that’s been proven to be effective. Ask a local garden center or Cooperative Extension agent to learn which herbicides will beat your toughest weeds.

For more in-depth information on herbicides, read Understanding Weed Killers.