Your guide to killing broadleaf weeds

June 19, 2015

A broadleaf weed is any undesirable lawn plant that isn't grass. They have leaves on stems, and contrary to the name, many have narrow rather than "broad" leaves. Dandelions, plantain, ground ivy and ragweed are also common.

Your guide to killing broadleaf weeds

Get to them early

Before broadleaf weeds start growing in the spring, apply a preemergent herbicide. It kills weeds before they sprout from seed and even kills some weeds that have just started to grow.

  • Spread the product on the yard between your first and third mowings in the spring. The manufacturer says a single application will last a full 120-day season.
  • This is as close to a one-size-fits-all magic bullet as you'll find for eliminating annual weeds. No other product on the market will target both broadleaf and annual grassy weeds and stop them from growing. It's available at lawn and garden centres (call first to make sure).
  • A 15 kilogram (35 pound) bag can treat up to 1,400 square metres (15,000 square feet).
  • Park your broadcast spreader over a tarp or on the driveway (grains may leak out, and a heavy dose of herbicide on the yard can kill even healthy grass).
  • Fill the spreader and distribute the herbicide evenly over your lawn.

Starting late

If a few broadleaves pop up in the yard (you can always count on a few dandelions), spot-kill them with a post-emergence herbicide. Look on the label for "broadleaf killer" then check to see which weeds it targets.

  • Some broadleaf herbicides also kill crabgrass.
  • There's no need to treat the entire lawn, just the weedy areas. Don't let them spread and create a bigger problem.
  • Premixed herbicides are OK if you have a small lawn and only a few weeds. Otherwise, buy concentrates to mix yourself — they're a better value.
  • Wait until the temperature is between 16° to 30°C (61°and 85°F), since the herbicide vaporizes too soon in high temperatures, and weeds don't grow fast enough in low temperatures to absorb the chemicals.
  • Mix the herbicide with water (follow the directions) and pour it into a small pump sprayer. Keep the nozzle 15 to 30 centimetres (6 to 12 inches) from the weed and spray until the leaves are slightly wet.

If you're too late

If your lawn has lots of weeds scattered over large areas, don't waste time spot-spraying individual weeds. Killing the weeds is as quick and easy as spraying the weedy area with a hose.

  • Pour a concentrated postemergence herbicide (the same kind you used for spot-spraying) into a dial sprayer and set the dial on the lid to the manufacturer's recommended mixture.
  • Attach the sprayer to a garden hose, turn on the water, and apply an even treatment to the weedy areas in the yard.
  • Apply the herbicide when the weeds are actively growing in the late spring and early summer.
  • You don't need to drench the weeds. A light misting will kill most weeds (if it doesn't, give them a second dose in a week).
  • Spray only on a calm day. Even a slight breeze can carry vapours that can kill plants (anything that kills broadleaf weeds will also kill flowers or decorative plants and could harm trees, so watch for overspray).   
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