GTA lawns come out of winter full of creeping Charlie, chickweed and crabgrass. Here's why it happens, which weeds are which, and what Ontario homeowners can legally do about it.
Household vinegar (5% acetic acid) will burn the top of weeds but does not kill the root. The weed regrows within 1 to 2 weeks. Horticultural vinegar (20% acetic acid) is more effective but will kill any surrounding grass on contact and can acidify your soil if overused. It is a non-selective burndown, not a systemic treatment. For lawn weeds, it is generally not the right tool.
Weeds fill in — they are plants actively growing into bare or thin areas. Lawn diseases leave dead grass without replacement. If you see greenery filling your spring lawn, that is a weed problem. If you see dead brown or grey areas with no growth at all, check for snow mould or fungal disease.
Clover itself is not toxic to lawns — it actually fixes atmospheric nitrogen into your soil, which feeds surrounding grass. However, clover outcompetes thin grass and spreads aggressively in low-fertility soil. More importantly, clover is a sign your soil needs fertility help — address the fertility, and the grass will eventually out-compete the clover on its own.
The window for most effective spring weed treatment in the GTA is mid-April through late May — when weeds are actively growing but before they go to seed. Treating after seed set stops the current plant but does nothing for the thousands of seeds already dispersed.