Why are weeds growing in my Ottawa asphalt cracks?

Weeds growing in asphalt cracks are a sign that your driveway needs crack filling and sealcoating — the cracks have widened enough to collect soil and debris, creating perfect growing conditions for opportunistic plants.

Asphalt cracks in Ottawa start small but expand rapidly due to our extreme freeze-thaw cycles. Water enters hairline cracks, freezes and expands by 9 percent, then thaws and allows more water penetration. Each of Ottawa's 50+ annual freeze-thaw cycles widens these cracks further. Over time, wind-blown soil, decomposing leaves, and organic debris accumulate in the widened cracks, creating a growing medium for weeds. Seeds from dandelions, plantain, crabgrass, and other hardy plants blow into these cracks and germinate in the protected, moist environment.

Ottawa's climate makes this problem particularly aggressive. Our temperature swings from -30°C in winter to +35°C in summer create constant expansion and contraction that keeps opening new cracks and widening existing ones. The heavy snow load and repeated plowing stress crack edges further. Spring snowmelt and summer rainstorms wash soil into the cracks, while Ottawa's clay soils provide nutrient-rich growing medium once they settle into the cracks.

The weeds themselves accelerate the damage. As roots grow and expand, they push against the crack walls like tiny hydraulic jacks, widening the cracks even more. Perennial weeds with deep taproots are especially destructive — they survive Ottawa winters and return each spring larger and more aggressive. Some weeds like tree seedlings can grow surprisingly large root systems that can actually lift and crack asphalt sections.

Immediate action needed: Pull or spray the existing weeds, then clean out all soil and debris from the cracks with a wire brush or pressure washer. For cracks wider than 5mm, fill them with hot-pour rubberized crack filler — this remains flexible through freeze-thaw cycles unlike hardware store cold-pour products that crack out within one winter. For smaller cracks, a quality cold-pour filler works temporarily. Once crack filling is complete, apply asphalt sealer to the entire driveway to prevent water penetration and slow future cracking.

Prevention is key in Ottawa's climate. Sealcoat your driveway every 2-3 years to keep water out of small cracks before they widen enough for weed groth. Address new cracks immediately each spring after snowmelt — small cracks are easy and inexpensive to fill, while large weed-filled cracks require more extensive repair.

When to hire a professional: If you have extensive cracking with established weeds throughout the driveway, or if cracks are wider than 10mm, professional hot-pour crack filling provides much more durable results than DIY cold-pour products. A paving contractor can also assess whether the cracking indicates base failure that requires more extensive repair.

Need help finding a driveway contractor for crack repair and sealcoating? Ottawa Driveways can match you with local professionals for a free estimate.