Your guide to using herbicides on unwanted weeds

Weeds that can't be removed by hand or mulched into oblivion can be killed with herbicides. Use them sparingly and pay close attention to safety precautions.

• When weeds are young, a natural or low-toxicity product, such as organic herbicidal soap, will often do the trick.

Save harsher chemicals for dangerous weeds such as poison ivy.

Vinegar is a completely nontoxic alternative to commercial weed killers. It is effective at killing common weeds — including the all-too-common Canada thistle — within their first two weeks above ground.

• Hand-spray in concentrations varying between five and 10 per cent.
• Try undiluted apple cider vinegar to kill off everything from poison ivy to crabgrass.
• Use it on a windless, sunny day and protect any nearby plants from accidental exposure.

• To improve your odds of killing only the plant you want to be rid of, cut a two litre soda bottle in half and place the top half over the weed you need to spray.
• Then direct your pump's spraying wand through the opening in the bottle and blast away.
• After the spray settles down, pick up the bottle and move on to your next target.

Take care when applying herbicides on the top of a slope if desirable plants are located below.

• Water runoff could carry the poisons where you don't want them to go.

Because a tree's roots are concentrated under the canopy, never use granulated herbicides to kill weeds there.

• Instead, remove them manually and cover the soil with organic mulch.

Reserve a single watering can, a sprayer and measuring implements for use only with herbicides.

• Water it immediately and thoroughly to flush the chemicals.
• Continue watering daily for a week to limit the damage.

Herbicides work best when temperatures are mild — 21° to 27°C — and the soil is moist. Don't apply sprays before a rain, which will wash them away.