How do I treat weed roots growing through my Ottawa asphalt?

Weeds growing through asphalt are a symptom of a crack or joint problem, not just a weed problem — treat both the plant and the opening it came through, or the weeds will return within one season.

Weeds don't actually push through solid asphalt. What's happening is that seeds are germinating in cracks, edge gaps, or deteriorated areas where the asphalt surface has opened up enough to allow soil, moisture, and organic debris to accumulate. In Ottawa's climate, this is extremely common — 50+ freeze-thaw cycles every winter progressively widen even hairline cracks, and by spring those openings are wide enough to host dandelions, grass, and in older driveways, woody plants with serious root systems.

Step 1: Kill the Weeds First

Before you do anything to the asphalt, kill the weeds at the root. Pull them by hand if they're small and the crack is narrow — get as much root as possible, because leaving the root behind means regrowth within weeks. For established weeds with deep tap roots (dandelions are notorious for this in Ottawa clay soils), use a concentrated glyphosate-based herbicide applied directly to the plant. Give it 7 to 10 days to fully translocate down to the root system before pulling. Don't spray on a windy day and keep it off surrounding lawn and garden beds.

For woody plants or grass that has established a mat inside a crack, cut the plant at the base, apply herbicide to the cut stem, and wait for full die-back before removing. Trying to pull a live, rooted plant out of a crack often widens the crack further.

Step 2: Clean and Prepare the Crack

Once the weed is dead and removed, clean the crack thoroughly. Use a stiff wire brush, a flat-head screwdriver, or a crack-cleaning tool to remove all debris, soil, dead roots, and loose asphalt edges. A leaf blower or compressed air works well to clear fine debris from the crack interior. This step is critical — crack filler won't bond properly over dirt, organic material, or loose asphalt.

Step 3: Fill the Crack Properly

For cracks under 5mm wide, a cold-pour liquid crack filler from a hardware store will work as a temporary measure. It's not a permanent solution in Ottawa's climate — cold-pour filler becomes brittle and fails within 1 to 2 freeze-thaw seasons — but it will buy you time until you can have a professional do the full repair.

For cracks 5mm to 25mm wide, use a backer rod (foam rope available at hardware stores) to fill the depth of the crack before applying filler. This prevents the filler from sinking too deep and wasting material, and it gives the filler a proper backing to bond against.

For cracks wider than 25mm, or for cracks that are actively spreading, alligatoring, or showing edge crumbling, this is beyond DIY crack filler territory. You're looking at a base problem or significant surface deterioration that requires professional assessment. A contractor can apply hot-pour rubberized crack filler using a melter — this product stays flexible through Ottawa's freeze-thaw cycles and lasts 5 to 8 years versus 1 to 2 for cold-pour products. Professional hot-pour crack filling runs $2 to $5 per linear foot in the Ottawa market.

Step 4: Seal the Surface

Once cracks are filled and fully cured (follow the product's cure time — typically 24 to 48 hours), sealcoating the entire driveway closes micro-pores in the asphalt surface, slows future crack development, and prevents new weed seeds from finding purchase. In Ottawa, sealcoating every 2 to 3 years is essential maintenance. A professional sealcoat on an average Ottawa driveway runs $200 to $500.

The Ottawa-Specific Reality

If weeds are coming through multiple areas of your driveway, or if you're seeing alligator cracking (a network of interconnected cracks resembling reptile scales), the underlying asphalt is likely past the point where crack filling and sealing will provide lasting results. Ottawa driveways built in the 1980s and 1990s — very common in Barrhaven, Kanata, and Orleans — are now 25 to 40 years old and frequently at end of life. At that stage, a full replacement with proper base preparation is more cost-effective than repeated surface repairs.

Need help finding a driveway contractor to assess your cracks and sealcoat your driveway? Ottawa Driveways can match you with local paving professionals for free through the Ottawa Construction Network.